Do Elival And Trileptal Cause False Positive Pregnancy Result?

hi im 35 And a Online Pregnancy Test says im 18 Weeks Pregnant my last Period was 2-8-16 they are always heavy im overweight and Haven t had a normal one but only spotting since then and now I have milk in my breast and ive had a chubby stomach since last week ivebeen putting on pounds like crazy but don t really have a solid stomach im on eliavil and trileptil my first blood pregnancy test was 2wks and 2days later then 30 days now I feel movement sometimes in my belly this will be my second pregnancy but first baby am I pregnant I hear that elival and trileptal can cause a false negative pregnancy test is it true im setting up a ob gyn appointment soon what s going on with me