Have you got the test done for the egg release (ovulation)? If so, how?
Has ultrasonographic ovulation monitoring indicated that you are releasing the eggs normally?
From your weight, I have got a strong doubt whether you are having
PCOS wherein the ovulation is not taking place.
The other cause for such obesity could be low functioning of thyroid glands (
hypothyroidism). Do you feel really hungry and eat properly, or your weight increase is in spite of low diet? So happens in hypothyroidism.
Please get your complete endocrine work up done and ovulation monitored. This will rule out or diagnose both these conditions.
One more delicate issue. Many a times due to over weight, effective intercourse becomes difficult wherein the penile insertion into the vagina is not there. Just have a look at this issue also.
Mind well, weight control should be done with adjusting the diet first and then going for exercises.
I have got a feeling, your weight reduction will help you becoming pregnant.