AFAIK
methotrexate and
prozac don't interact other than being one more stressor on the kidneys and liver to get them both out of your system.
You might generally feel a little "blah" from the methotrexate, it beats up your immune system, so that is expected. It generally doesn't last beyond the 2 days of the week (day you take it, day after).
If you are feeling "blah" all of the time, get him to run a blood tests for liver enzymes just to make sure everything is okay -- it's a good idea to do that regularly with methotexate and to get a chest x-ray every 6 months in the beginning and every year after just to make sure it isn't causing problems.
Good luck.
Are you numb yet? No. AARRGGGGGHH! I told you I wasn't numb! Sorry, I didn't believe you.