Although some women are capable of a purely internal orgasm and far more enjoy penetration, if you were going to find your bliss poking about in there, you probably would have already.
As for the drugs, they may indeed be inhibiting you. Many people find that the effect wears off over time, but you've had time and it still isn't working. I suggest trying the clitoral route (your fingers, a vibrator, a shower massage, his fingers, his tongue ... you get the picture) while also putting your doctor on notice that you may need to lower or change your medication soon. Perhaps remind him or her that never ever having an orgasm is a depressant in its own right.
Andrea Nemerson has spent the last 14 years as a sex educator and an instructor of sex educators. She rarely has That Clinton Problem. Visit www.altsexcolumn.com to view her archived columns.