I take Wellbutrin (Bupropion) XL. My anxiety didn't get any worse during the first few weeks, and by my recollection, it did take me about 6 weeks before I could actually notice positive results. It might have been sooner, but it was a sort of slow realization that my anxiety issues had improved.
However, that effect on me was short-lived. About 6 months after beginning Wellbutrin XL, I plateaued and felt like I was slowly sliding back downhill. I spoke to my doctor, and he increased (doubled) my dosage, and that's where I am now. But... now I'm sort of rocking back-and-forth between good days, and bad days.
My problems are anxiety, depression and OCD, and they all feed off each other. I'm sure you know what I mean. It can start with an OCD episode, then anxiety begins, then the depression kicks in. I am better with the medication, but I want to try supplementing it (was actually popping on here to research just that).
If it were me (and you can totally dismiss this), I would try to stick with the Wellbutrin for a few more weeks. I'm not sure what the difference is between the SR and the XL variants (I think it's "slow release" vs "extended release"). I takes weeks for these type of medicines to "kick in" as it were, or at least that's how my doctor explained it to me. But above all, keep your doctor in the loop -- let them know how you're feeling and if you think it is or isn't working... or if you need to change your dosage. All bodies and minds are different.