My Frenchie wasn't feeling 100% yesterday, he was a bit too quiet and later in the afternoon was sick a couple of times (quite watery and smelt sour). I didn't take him out for his walk last night and when he sat next to me  for a cuddle i noticed that he had developed large blistery swellings all around the edge of his mouth and under his chin. I gave him some piriton which within an hour started to reduce the swelling and this morning is now completely clear. However he still isn't his normal happy,playful self and has been sick again but this time was bright yellow water. He hasn't had a change of diet(hasn't eaten  since yesterday morning), he is drinking as normal.
I would appriciate any advice about the swelling around his mouth and if anyone has any suggestions what could of caused it.
Thank-you.

I would get him to the vets to be checked out to be on the safe side as he is still not right. It could have been a sting but it is difficult for people to make assumptions on what could have caused it based on not being able to see him or being a qualified vet :-)

I would go to the vet immediately. It may be nothing, but best be safe. The reaction around his mouth and chin might be to something irritating or even poisonous, particularly as he is being sick. In your shoes I would not delay. 

My friends frenchy swelled around the mouth to this summer- but she was chasing wasps- could yours have gotten stung?

My sisters dog needs to have eppic pen cause she's alergic to stings- something she has to have on her at all times.

Hope ur pup is doing better...

Vets NOW - no delay this may be urgent. Hope I am wrong but if I am right then you will be pleased you acted NOW

Sounds like she's eaten something or been stung, I agree - best get her to a vet to be safe.