I had a similar experience a few years back, I bought a bike a few years back, it killed my ass. I think I was done within a quarter of a mile. After a few days I
decided I did not want to throw away the money so I tried again. This time the
bike not only killed my ass, but it bucked me. (chain locked up and I went over the handle bars onto the concrete) I was so pissed I traded the bike for a custom
knife and did not ride for ten years. Finally, about nine months ago a friend gave
me one of his bikes which had a miserable seat which I replaced immediately.
After playing with the seat angle... height... yatta yatta yatta I was good to go.
I wished I had just made a few adjustments years ago and never stopped. I got
a new bike, made adjustments, added a Serfas seat cover, and ride away.
The moral of the story, proper fit it the key.