What's the next step?

Okay I recently did a poll of the likelihood of a false negative beta HCG blood test at 12 weeks post sex. About 30% out of 29 said it could happen (as in, common). My result was less than 1

This was supposed to be the final step in me determining if I was pregnant and calm my anxiety. Now I'm not so sure

So far I've

•Had three withdrawal bleeds, heavy in nature.

•10 negative urine tests

•Beta HCG that measured me at less than 1.

But what now? I feel like this still isn't enough to prove it. Should I consider an ultrasound? My stomach has been having weird twitching