My Sheltie has been dropping blood for a week now, (not very much though), i just wondered how long it will last please.
Also other dogs don't seem intrested in her at all (thankfully), but i had been led to believe that if i went out with her we would be mobbed by amourous males, is this unusual/normal. Many thanks.

Yes, it is normal.  A season will last around three weeks.  You have the first stage now, then the blood will go and that is usually when she is most interesting to other dogs. A bitch is usually mated from around day nine to day fourteen, although this can vary.  She will still be giving off scent until around day 21.

Don't let her off the lead during this period, I usually just walk mine around the block for a short walk, but there are not many dogs around where I live.  If you have a large garden then you can keep her in for the duration to be on the safe side.

At the end of the season, give her back end a bath before taking her out.

If she has been bleeding for about a week you probably have another 2 weeks of your bitch being in season.The reason you are not having problems with males at the moment is probably beacasue she is not ready to mate.Bitches are usually receptive to males when the bleeding stops...so please don't think that as soon as the bleeding stops she has finished her season...quite the opposite!
You are beeter off keeping her away from males for 4 weeks afetr the onset of her season to be on the safe side
Archer