I Have Hypothyroidism. I Track My Cycles, Because They're Irregular.

I have hypothyroidism. I track my cycles, because they're irregular. The tracker I use is usually pretty exact. The longest cycle I ever had was 63 days and that was once, 3 years ago. Currently I'm on cd 78. I had unprotected sex around the time I should've been ovulating. I've taken several home pregnancy tests. I've had three positives and several negatives, even after the strong positive. I keep getting light headed/dizzy. (Not like when somebody has low sugar, more like pressure in my head). Could I be pregnant despite the negatives?