Motivation and getting over pain?

I've been struggling to put this up for advice for fear of sounding like I'm just complaining but oh well, I currently have Scoliosis (have had corrective surgery but still causes some pain) and also because of my weight it has caused strain on my legs I'm not sure if its anything else but i believe that's just the main reason.

Because of this i have found it difficult to keep up with exercise for long periods of times. But this time i am confident that i am going to lose this weight although i am still unsure how to go about starting ( I am using MFP to track intake and slowly working on my bad habits of eating and drinking mainly sugar intake is my biggest weakness on this part) but as for exercise i'm thinking of just starting with the gym. anyone have any thoughts or advice on this subject.