needs motivation & help with weight loss

I am 26 years old and I have had 2 kids. I am 5'7 and I used to weigh in at 130lbs. Now I am weighing in at 250lbs!!! I have hypothyroidism and have been regulated on my medciation. I have joined a gym, even paid for a trainer but for some reason....I just don't go. I am terrified of being a mother who cannot keep up with her kids. I was working out 2-3 times a week for awhile in the begining but didn't lose any weight. I got discouraged and ....just haven't returned. Any advice to get myself jump started to get back on track. My mother is overweight and just got diagnoised with type 2 diabeties. I don't want that to happen to me. I know I need to get myself in gear...but I just can't seem to do it alone...Any advice?