Sounds like you may be lacking in base conditioning.

And if you are injuring yourself easily and with all the stress you are carrying, I think having a good stretching workout of 15 minutes or more is a must. Just a gentle slow and easy stretch.

If your muscles are knotted up or tight, you will get hurt so stretch them! then add core body work to strengthen your core.

Brisk walk a mile then work up to two mile, continue to do stretching exercises. Once you are reasonably okay with it, then try cycling. Also ride in lower gear. 80rpm and below and you are mashing and you may injure your joint.

And when you are riding your bike, make sure you spend first 3-5minutes at a very leisurely pace. Then work up to your workout intensity. Way too many start off way way too hard. And cool down should also last minimum of 5 minutes. It gets longer for longer workouts. Easy ramp up and easy ramp down.