Sorry to hear of your struggles. Yes, I can identify with your frustration. I used to run half-marathons at a decent pace, until cancer treatment nuked my lungs. For several years I worked hard trying to come back, envious of people flying by, and embarrassed by my presence in the back of the pack. Eventually I accepted that my competitive days were over, and I took up cycling. I now enjoy riding so much that it doesn't matter that I'll never be fast. That's what I tell myself, and then I see or hear of women riding fast, and I still envy them. Once you've been fast, it's hard to accept slow. But when I'm riding, I love it, no matter what.

I hope you get to a doctor, or doctors, who can find the source of your slowdown. Perhaps there is an easy "fix" for your problem, and you can get back to your old self. It's only been a month, so don't despair, and definitely don't give up. Pursue the cause of the decline, because something is going on with your body. The sooner you get in to the doctor, the sooner you're on the road to recovery.

Best wishes for good health and good riding.
Jan