How long ago was your surgery? It sounds like maybe you're not very far out. Most people feel pretty crappy for the first couple weeks (or more), but it does get better, I promise!
The first time I tried to take my Effexor post-op, it made me puke because it should be taken with food, and I didn't have enough in my sleeve to make it tolerable. I also found that I metabolized it differently and would get to feeling really weird (Effexor users call it "brain zaps") when it got too long in between doses. So what I did (with my psychiatrist's OK) was to cut my pills in half and take one in the morning and one in the evening. Later I was able to get a smaller dosage pill so that I can take one in the AM and one in the PM. My surgeon said that it was OK to take them right after I eat with a little sip of Water, so there is something in my stomach when I take it. I don't know what medication you were taking and if it can be cut, but that may be something to bring up to your doc if you were otherwise happy with the meds.
I also take Effexor XR and thought I would have an issue with it as well but thankfully did not. And argh I know all about the brain zaps. So far it seems to be doing okay with me, I am 7 days post-op. Do you feel the drug works better for you than before overall since WLS or the same?