Important GERD and treatment question. Can you help me please??? ?

I have been sick for a long time now (about 4 years now) I had lost weight and have been having really bad tummy aches and constatnt nausea. And when I lay down at night I would get "wet belches". I would burp and taste vomit in my mouth but I never actually would vomit. I would also get diarreah sometimes. But my symptoms (nausea tummy aches) would sometimes increase during my period.My doctor finally diagonsed me with GERD after asking me a few questions. I had been tested for ALOT of crazy things in the past but all came out negative. So I was so relieve to hear a diagnoses. But the doctor told me to take Zantac but it made my tummy hurt 10x`s worse so I stoped taking it after 2 days. So now she switched me to Prilosect OTC. Now I am so scared of taking medications. I never self medicate for anything. Not even a common cold. And my first medication was for a UTI and the antibiotics made me feel really sick and so did the Zantac. So my medication history was not a good one because it always made me sicker. Thats why I have not started taking the new medication yet. So my question is, how bad are the sideffects of Prilosec OTC? Since im using it to treat my GERD symptoms instead of heartburn would it still make me nauseated? Thats my main concern now. Im almost always nauseated and having tummy aches so I really dont want to take anything that would contribute to that. I just want it to stop once and for all. I just want to feel healthy and normal again. I really dont want the pills to make it worse. If you have GERD and take Prilosect OTC please tell me how it worked for you and what I should expect for me. Also if there are any other GERD medications out there with little to no side effects that you know of and or have taken please do educate me on them. I know most meds will have side effects but I just want to know what I may be in for.Thanks for the answers in advance. Also why do you think my period makes the nausea and tummy aches worse?