I once felt a lump in my head, which I'm sure everyone has...and I to convinced myself that I had a brain tumor. I was obsessed over the situation to the point that I was nauseous about it, I thought I was going to die. It sounds to me that staying on the Zoloft is probably your best bet, I know that medication helped me.
There is absolutely no possibility that you have given yourself a brain tumor by your use of Zoloft....
No don't worry about it. Stay on the Zoloft for now. It seems you may suffer from a bit of OCD/anxiety.
gre: the brain tumor, it is impossible to generate a brain tumor from taking zoloft - re-assure yourself. perhaps you had this underlying fear all along re: the brain tumor.
I had the same fear starting when I was 12 after reading "Death Be Not Proud" by John Gunther, written as a memoir for his son who was a student at Deerfield Academy and struggled with and eventually died of a brain tumor.
I was asigned the book in english class and became so wrapped up in the details that i convinced myself that I had a brain tumor also - It wasn't until i saw a psychotherapist in my junior year of college (8 years later) and admitted that i thought I was dying of a brain tumor for the past eight years that I was able to dismiss the whole 'crazy' thought.
best wishes..