5'8", 190 lbs. Goal of 135-155. Motivation help?

My doc says I need to lose at least 30 but more like 50 lbs as soon as possible for my health. I have hip dysplasia and the extra weight I've been carrying since my daughter was born is causing my hip joint to deteriorate. If it don't lose the weight, and soon, I'm looking at a hip replacement surgery. My problem is that I work at a gym, so I'm not all that motivated to spend any extra time working out. Plus I have no idea what is really the most effective. I try to do a mix up of cardio and weight lifting but I'm very weak and out of shape, so I get down on myself and give up easily. Any suggestions for motivation or how to get going in the right direction? According to MFP, if I stick to my diary goals then I can lose 2 lbs a week, but I struggle to lose .5 lbs a week. HELP!