It may be an ovarian cyst. Cysts can stop your monthly cycle and cause pregnancy symptoms because of the hormones they produce. I suggest you ask the doctor for an u/s to confirm that.
Cysts can also cause pain, much like what you are experiencing.
Your doctor will probably prescribe you provera or prometrium to start your period again. If you do have a cyst, they will probably prescribe you birth control pills as well.