Sweetie, pregnancy symptoms usually don't even start until weeks 6 or 7 of pregnancy. The pulse in your lower abdomen is your own through a major artery that runs through there. You can not feel a baby's heart beat from the outside of you. :>)
I would say you are having a very long cycle and not pregnant. And PMS will last a long time if your cycle is extra long and symptoms you describe could be that as well. Hypothyroidism is something to ask your doctor about as it can cause all of this. Your tests indicate you aren't pregnant. Talk to your doctor for other reasons for your symptoms. good luck