Help...Do you think I should worry.

5 years ago when i had my first baby I had a migraine so bad I ended up in the ER with stroke symptoms turns out i had pregnancy induce migraines i was 7weeks along.

fastfoward 5 years i have not had a migraine since trying to start birth contol after said baby (big mistake) this was 4 years ago.

now i have had headaches since march 12th which should have been the ovulation part of my cycle, a week after they started i had a week of migraines.

i took 4 pregnancy tests all negative and my husband had a vasectomy (1 year ago), i was prescribed topamax from my nerologist, but now im wondering why the headaches. could i be newly pregnant and just not turning a test? if i take this drug which causes birth defects in babies and i do turn out pregnant would it be early enough where it shouldnt matter? should i wait to rule out pregnancy or am i just being paranoid?