Ibs-d, lethargic, and can't lose weight or exercise. how do i get over this?

Slowly and carefully: You just need to start slowly and build up on a constant but persistent basis. Also, keep a careful inventory of what you eat. There are good apps that can track your daily calories and this can be very helpful. There are also medicines that can help. Also, very important to diagnose and treat any underlying diseases such as sleep apnea, diabetes, etc. Please see your doctor.