I mated my bitch 3 weeks ago last Saturday and Monday. Last time she had a large litter (15) and I was sure quite early on she had taken. Is there nothing that you can go on in the first few weeks? When on average do you scan.
She i a real foodie so I am worried about over feeding her but don't want her to feel hungry either. I hate this stage the most... just wondering.

i didnt feed any different at 3 weeks even tho she wanted more she was scanned at 4weeks i uped her food at 7weeks slowly her pups are 2days old and shes looking great not thin at all shes a toy breed and had 5 good size pups, i wouldnt over feed yet.

Food isn't normally increased until the 6th week and then only slowly to about half as much as normal by whelping. 

On occasion I have doubled the food by whelping time, as I go on how much coverage there is on the body, not how fat the pregnancy makes them look.

With my won bitches within a day or two they are eating about 4 times their normal amount, and if they have more than 6 pups they are eating about 5 times their normal amount.  so a kilo of dry food as opposed to 200g.

I'm always amazed when I read in books about doubling the food intake in the first week, as mine would starve if that is all I did.

So what I am saying is monitor the bitches body condition.

Yes I would have to watch this ones weight anyway but I was wondering about other signs if anyone thinks there are any as of course it is indicated that there will be none for quite a few weeks anyway. I am not a novice it is just sometimes you just seem to know,like her last time, and other times although eventually there are puppies, you have no indications at all.
My OH doesn't want to scan until 5 weeks so it is worthwhile.

My girl has just been confirmed pregnant. From 3 weeks she was off her food. her nipples were slightly enlarged and pinker. Now at 5 weeks she id definitely looking thicker round the waist.

Often the behaviour changes are the first things I notice. With my latest pregnant bitch I suspected within days as she changed her ways. After 2 weeks I was absolutely certain, then at 3 weeks the clear discharge started and her teats got harder so just stroking her you could feel the difference. Just days after being mated she became really cautious. Would not run as fast, did not want to go outside with the other dogs, stayed back when everyone else was running around in excitement, it was like she was being careful to protect her pups and avoided being slammed into. She's still acting that way (she's 5 weeks now). After 2 weeks she started eating slower and didn't finish it all.

But I've had other bitches where I had no clue at all until the scan at 4 ½ weeks.

My first ever litter was born a week last Tuesday so it was all new to me. I had a good incling quite early on that my girl had taken, mainly by her behaviour changes. She quietened down quite a lot and became more clingy. Her appetite went through the roof, but I was warned by my mentors not to succumb to this for fear of large puppies. I did not increase her food intake until 6 weeks but this did not prevent huge puppies, resulting in a c section as the first one was stuck.
I had her scanned at four weeks. At about 3 weeks, her teats enlarged and became pinker and got a slight blue tinge round the base of them. I was told by several people that this is a good give away, so maybe your girl has a few of these signs?
It was so hard for me to be patient in waiting or the scan to confirm pregnancy so I hope your scan comes round quickly to put your mind at rest. Meanwhile, a few signs may appear :)

Trouble is with looking for signs, they have they same if they are having a phantom pregnancy too.  So even if mine were showing all the symptoms, I wouldn't go on just that.  I need the scan or puppy movement before I actually believe it!!lol  Also, even after the scan, I don't count my chickens.  So much can still go wrong that I don't count on a pup or litter till it's on the ground safely(and for the next few weeks too!!) I'm a bit paranoid.hehe.

Never gets any easier does it. That waiting and wondering. The reason why I thought she was last time was she went quite quickly from being a truly good eater ( finishes up anything anyone else might leave ) to literally snatching anything being offered. It was the big litter.
I know I am being premature - I'll carry on sitting on my edge until the scan..
I know what you mean too as I lost an entire litter once that was said to be a large litter at 5 weeks and was reduced to 3 dead puppies at full term so like you I never assume anything until they are born and then survive for the first week or so. Then I start being optimistic.