For swimming, it’s easier to tie a bunga with your keski, but the material will absorb water hence your head might feel slightly heavier. And yea, I tie a 2nd keski around the waist incase the 1st separates the body.
Wear a smaller 7inch & tie the gatra tightly around the waist. And wear a swim shirt over your upper body.
What has your physician said about cycling at the gym?
Its a cardio and it helps in burning fat.
Also, if you do the same exercise all the time, you may lose weight initially but then the progress declines because the body 'adapts' to the activity.
Compound exercises is the way to fo.
Loosing weight requires focus on 2 areas.
Exercise (weight training+cardio) and carefully planned diet. (no, you do not have to starve yourself!)
let me know what is your diet like maybe I can make recomendation.
As a start delete sugar and rice from your diet totally.
ਸਤਿਗੁਰਬਚਨਕਮਾਵਣੇਸਚਾਏਹੁਵੀਚਾਰੁ॥