can hypothyroidism cause a false negative on an hpt?

I had unprotected sex with my boyfriend the 2nd. On the night of the 16th ihad very light spotting. Could have been implanation. I took a hpt 2 days ago and this am-both false. I’m irregular but usually start by the 20th.. I’ve had nausea, funny taste in my mouth and light cramping. I also have hypothyroidism, which I take synthroid for, so I don’t kno if it would cause be to have a false negative or did I test too early? Any advice will help. THANKS!