WUN,Hello and I am sorry to read of your problems. I am the one on 300mg of Effexor and I have to admit that I noticed some increase in anxiety with the dose increases but no stomach problems.
I do take my meds every morning with food so you may want to be sure to take your meds with food, not shortly before or a bit after.
Also more time may help and if it doesn't do check in with your Dr.