Can't seem to lose last 15-20 lbs?

I'm 5'9 and weigh 164 lbs. Had a baby 10 months ago and gained about 40 lbs or so. I have been working with a trainer doing weight/strength training 3 times a week for 2 months. Running about 2 miles a week on my own. I'm not really dieting, but I eat pretty well during the week. On the weekends, I admit-I cheat a little. But I don't gorge myself or go crazy or anything. I just can't seem to lose this weight. My trainer says its what I eat, but I'm not eating that bad! And whenever I do actually diet, I still can't lose the weight! I just can't break past 164 lbs. It's driving me crazy. Does anyone have any suggestions? HELP!