What Causes Pregnancy Symptoms With Negative UPT?

I am 40 years old. I had unprotected sex twice in December (withdraw method). I am experiencing alot of pregnancy symptoms, but all urine tests come back Negative. I have had my liver, kidney and thyroid checked last month and all are good. I had my hormones tested lat summer. I am still having monthly bleeding although not like my regular periods. Is it possible that I could be pregnant or just a coincidence and I am starting peri menopause?