Thrush is very common to get when on antibiotics, especially any type of penicillin drugs. All you have to do is tell your doctor and they can prescribe a one pill cure called Flagyl. Just tell them you have thrush and they should do that for you. It is a miserable thing to have. I get it every time I take Amoxicillin.
Your mom is probably right. Thrush can be very painful before the obvious symptom of a white coating on the tongue shows up. Try taking acidopholus capsules. That's the active ingredient in yogurt that helps with any kind of yeast overgrowth, which is what thrush is - yeast. They're available at any pharmacy or health food store. Stay away from highly seasoned foods in the meantime. I had thrush after a round of IV antibiotics and anything with pepper was intolerably painful!