weightloss blues

so i have been off cymbalta for a few days. defiently feeling weird and off because of that. i will go back on on thursday though so no biggie.. mostly feeling a little down about my weight. dont want to post about it on the weightloss blog as i want that to be positive. but really, i have sooo much weight to lose i am starting to think i wont be able to do it. ever. no matter what. the goal i have right now, which i know was overweight still, but i felt really good when i was at that weight. after reading about BMI's i realize that over 30 is considered to be obese still and I would be like 32. so then i was playing around with it and to get to just slightly over weight with a bmi of like 29 i would have to lose over 300lbs. (yes i havnt come right out and said what i weigh, its humilating...but you can kinda guess by this post i guess...oh well) 300lbs! is that even doable??! like ever!?? i wont give up, but i guess its never going to be my future to not be obese. why did i ever let myself get this big????? sometimes i hate myself for allowing it to happen. i am worried too that it will be harder on bipolar meds, all the side effects for my meds say weight gain....i really hope that doesnt mean i wont be able to do it. feeling frustrated today. could use some support.