I 'm 50 year old female asthmatic weighting 220 pounds. I am on predinsone every month.

You need to talk to your doctor about the possibility of weaning you off the prednisone and getting better control of your asthma with long acting/short acting and maintenance medications.  While doing that - find out if you can get a consult with a dietician to work on an eating plan and see if you can get a "rehab" referral with the goal of getting some help with your exercise program.  As a somewhat "fragile asthmatic" you might have insurance coverage for these if requested by your MD.

Also - even 10 minutes 3-4 times a day is a good way to get aerobic walking activity and not tax yourself during one long exercise effort.