I Think I May Be Pregnant. I Have Took Multiple

I think I may be pregnant. I have took multiple urine tests(10) that are negative. And I have been having a regular period that is very heavy flow for the last few months. However, I have been exercising but my belly continues to grow. I have actually gained 8 pounds since exercising even though I cut down on portion size. The growing belly is the only symptom that I have. I do have IBS AND ASTHMA.