swelling around shoulders

I can't really tell, but I think Mosley is swollen between her shoulders. I noticed this a few days ago but wasn't sure. Then I could really easily feel the microchip and became concerned. I posted on another thread that it might be because she was microchipped about 2 months ago (because the microchip seems really close to the surface of her skin-not like usual). Well, now I'm wondering if it could be some kind of reaction to the Revolution I put on her about 2 weeks ago for the first time (maybe ever, but for sure since I've had her). If she is swollen, maybe that's just pushing the microchip closer to the surface.

Has anyone had this happen? I'm going to call the vet, but haven't been able to yet. Please respond with any info. Thanks so much!
Lauren

Lauren, usually a reaction to a spot on flea treatment happens right away, not weeks later. I have never heard of a reaction to a microchip, but I suppose it is possible. Perhaps the needle got dirty? I would definitely call the vet and find out what it might be-