Having Pregnancy Symptoms, Negative Home Pregnancy Tests. What Should I Do?

Hi i am writing because i am very confused as to if i'm pregnant or not. My stomach has been growing the past weeks so much that i look 5 months pregnant but i haven't gained any weight. I had nausea for a week two weeks ago but its gone now. I now have back pain every morning, constant headaches, tender breasts, mood swings, tiredness, cravings and my stomach is huge. I have taken two home pregnancy tests and they say negative but i feel pregnant as i have a son and i feel the same now as i did while pregnant on him! My doctor wouldn't do a test as he says home pregnancy tests never lie but I can't figure out whats wrong with me. Please help