Negative reaction to resistance exercise, can anyone help?

Hello all

I'm a 34 year-old male. Whenever I do light jogging or cycling I have no negative

reaction, but when I do anything involving resistance eg weight training (i.e. anaerobic

exercise), I feel great for a few hours, then after that I become irritable and stressed

for no apparent reason for the next 3 or 4 days. I also sleep very poorly for those days

as well and feel really sluggish and lethargic.

The standard blood tests (which looked for probems with my thyroid, for example) didn't

show anything unusual.

Anyway, it would be really good to hear from anyone that might be able to offer some

help for this really frustrating problem. I'm supposed to be doing knee strengthening

exsercises following a cartilage operation but I can't due to this reaction to

resistance exercise and I love doing weights.

Thanks!