Please please help

Hi all!! I am 18 and currently have a 4 month old. I have been on the pill lately so I dont really have periods so I cant tell if I'm late. I just have a question. I have been feeling super "pregnant" extremely nauseous (especially after I eat) bad acid reflux, bloating, and heart burn. Exactly how I felt when I was pregnant with my son. I took 2 pregnancy tests the other day and both came up negative. I thought I was sick and have given it more days but I'm not getting any better. Is there a chance I could be pregnant but getting negative tests or could it be something different? Thanks so much!!