Yes, it is possible. Someone with hypothyroidism isn't going to ovulate regularly and that is why they/you have long cycles--- but they do ovulate at times (two weeks before they bleed for a period) and if things happen to fall at that time when intercourse happens, pregnancy can occur. However, do keep in mind that hormones need to be in balance for a viable pregnancy and many with hypothyroidism have hormones out of whack. (I had hypothyroidism for a year and a half, so have been there myself). I had periods every 3 to 4 months during that time. I doubt you are pregnant. You've had negative tests. Do you work with your doctor for the hypothyroidism? Mine self regulated but I was all set to see an endocrinologist right before it did that. Talk to your doctor about it. good luck