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If you have only mildly raised SGPT no other health issues, it is right way to repeat it after 3 to 4 week to see if it is normal or not.
It is good to do regular exercises but not fanatic please do regular gym not very heavy one start from cardio exercises.
As you have gained weight there may be some fatty liver
which can cause SGPT rise there are many other causes of such rise but take care of diet also take less fats and avoid high calories in diet.
which also depends on your age.
You may take 3 to 4 month to lose weight but it is more important to maintain that .
Remember pevention is better than cure.