Day 3 Exercise

I feel like I have a different experience with exercise than others. I regularly walk 20 minutes/day and generally, although it's somewhat painful doing it, I feel better after. I swam this morning and felt pain while doing it, maybe felt worse after--although I don't think that's usual. My pain is in my legs and feet and often, arms. I think I could, maybe should, push myself more physically--though not too much. I'm 74 years old.