I've Had 13 Negative Pregnancy Tests But Am Paranoid About

I've had 13 negative pregnancy tests but am paranoid About false negatives; when can you accept the result? I didn't really miss my period, it came on time, lighter than normal but one night of very extreme cramps, plus clots but I bled in total for 5 days as normal. But I have some pregnancy symptoms / ovarian cyst symptoms and don't know which applies to me