21 days late and still negative

So I'm feeling nauseous about Everytime I wake up or wake up from a nap I constantly am dizzy I've had some spotting like a week ago didn't last a day it lasted a couple of hours then stopped I'm still getting negative tests maybe I ovulated later ? Maybe the tests I've used are faulty idk I'm nervous and very worried due to the fact that I'm still on keppra a seizure medication and idk what to do I went to the doc like two weeks ago they said I'm not pregnant idk what's going on I just need some advice on what to do I'm very worried about myself and the possibility of me hurting my baby causing it birth defects because of the medication what do I do please help!!!!