thyroid & pregnancy? false negative? hellp.

So my last period was Aug. 22 & was for 5 days. Just as it has been for the past two years since I had full thyroidectomy. Now I take hormone replacement daily. Boyfriend and I have unprotected sex often & weren't very careful when we first became intimate. my symptoms just get stronger by the day I am 99% sure I'm pregnant I just have this feeling.. Ive taken 3 test all negative (that I could see) I had strong cramping Sunday, & Monday with no bleeding so I went to ER & they refused to blood test or anything because my urine was negative. Sent me home and gave me two days off. Tuesday I had a bm and one large creepy looking clot of sorts came out no bleeding. Then I started having brown spotting and have had it only when I go pee (which is too often) & it's pretty much subsided. OB/GYN apt on Monday. Nurse said didn't sound dangerous but to keep my apt. Is there ANYONE with thyroid hormone therapy that can give insight?!