Have you had an internal ultrasound done that may indicate a problem in or around your uterus. Even possibly a laproscopic surgery to investigate into your problem. Your symptoms sure do identify a pregnancy. There was a case that a woman was pregnant with twins but only one was identified. Maybe this would be possible with one. However, I've had a grapefruit size ovarian cyst that caused me to gain weight,my breast enlarged, and I was extremely tired. Only until I was extremely uncomfortable did my doctor locate the cyst by internal exam and internal ultrasound which was cause for immediate major surgery. You have my prayers to locate what's wrong soon.