I had unprotected sex and am on lo loestrin fe. i also take wellbutrin, (bupropion) topimarate, phentermine.can the meds lower effect of bcp & could i be pregnant?

Not impossible: Not likely unless everything was just 'so'. The time of ovulation, if in your case the Topiramate did lower the effectiveness enough, etc. The other meds don't present a problem. So, if you miss a period - do a test and find out if the happened. Learn your fertile time and use protection then - consider alt to either the seizure drug or the pill. Discuss choices w/ our Dr. Best!