Red Areas on Soft Palate after Oral Sex

My girlfriend and I have been together for some time now and we tried oral sex for the first time about a year ago. The first time it happened was unprotected and afterwards these red areas on her palate appeared. The areas are reddish, have some small dots and are painless. She has little discomfort but no pain at all..and the areas disappeared after 2 to 3 days. We have no idea what it could be since she has gone to her doctor and dentist and has not gotten an answer. She also got blood work done for Strep Throat and Mono but it came up negative. I recently had blood work done too for STD's and it came up negative. We're trying to figure what it is since we had oral sex again a few days ago and the areas appeared again. Any possible reasons why this is happening??

[gracefromHHP]

This sounds like irritation from performing oral or even petechiae from sucking too hard.  I would not suspect that this is a std of any sort.

grace