Newer research has shown that with the exception of rifampin (for TB), antibiotics do not affect the effectiveness of the pill. So you're fine :-)
I happen to have a 2006 copy of the nurses' drug guide. I looked up the keflex, and found nothing on it that says it will alter your birth control pills. I could not find the other drug. Does it have any other name, like maybe the really long scientific name? I have taken keflex before an dI didn't have any kind of warning on the bottle that says it would decrease my birth control pills' effectiveness. I'd sday you are safe as far as that goes.
I would say if your doctor seems to think its ok then it should be. If you are worried then take extra precautions. Condoms or not having sex. You can always ask ur GYN or the Pharmacist too.