You wouldn't have to wean off sertraline after just two doses, unless you've been taking an SSRI prior to that and moved straight over to sertraline. Then a taper would be needed. There's a user on here who knows way more than me about these medications who will hopefully be able to offer you better advice than I can, but what I will say is that 50mg is quite a low dose of sertraline. When I was on it, I was on 100mg and had the option to go higher still. Also, two doses is not enough to really make much difference, good or bad. I don't know enough to say whether two doses could trigger the side effects you experienced, but I do know that it isn't anywhere near enough to say whether it is helping or not. When I took it, I experienced very difficult side effects that kicked in after about a week, but once those side effects went away, it really helped me, but I think I'd been on it about six weeks before I noticed it beginning to work for me.