Ok so im diabetic and have pcos but why is this nessasry exactly?

i got diagnosed with type 2 diabetes in december. since then ive been on metformin but i havent been able to take the full dosage as the nausea and vomiting was prevalent all day everyday and ive got to work. the doctor says because of the pcos i need to be on metformin but i explained to him yesterday that the side effects are that bad that im frequently skipping doses when ive got to work or go out. since i was diagnosed ive lost 2 stone in whieght but my blood sugars have continued to rise. when i talked this over with the doctor yesterday he was like we need to up the dose but not much chance of me doing that when i constantly feel sick on it. so then he was like would you consider a gastric band. i dont understand why he wants me to have surgery when i am losing whieght. does a gastric band improve sugar levels?