Could this pain be from taking Zoloft?

I have been on Zoloft a few months now. It worked right away and I felt
great. But it has lost it's effectiveness. I am on 50mg, do I need a higher
dose?

Also for a few nights now after taking my Zoloft tablet, I have been in
agony with waves of heartburn type pain, but no acid came up. The pain was
in my chest, and came in waves of burning. It goes by morning, eating makes
it worse, and sleeping upright makes no difference. It just doesn't seem
like heartburn.
I have never experienced anything that painful even when pregnant.

Maybe I have an ulcer, I don't know. This sucks along with my wisdom tooth
removal (