Yeah, we have to be careful with exercise. I was recently told that I should work on increasing frequency of exercise first rather than duration. For example, if you can do a 5 min walk without symptom issues you're better off trying two 5 min walks spread over a day rather than a single 10 min walk.

I definitely have been guilty of going to increased duration before frequency many times and in every case it's been an issue. I'm currently working on doing frequency instead.

Also, remember on those days that you feel "good", don't try and do too much... again, I've been guilty of doing this and it's always a set back.

Regardless of all this, it's good to hear that you can do some exercise!