Similar here, I had my first baby in July and put on over 3 stone with the pregnancy. I also suffered from PND and had a lot of anxiety leaving the house which didn't help with exercise or eating healthily!
I found that antidepressants gave me the boost I needed to make more lifestyle changes.
Try getting a fitbit, this is a good motivator and helps you make healthy choices, like walking instead of getting the bus so you can get more steps.
Try using the app "myfitnesspal" to track calories. I find this app invaluable and keeps me in check.
Try workout dvds so you can fit in a quick 30 min exercise while baby is asleep/entertained. I like Davina Mccalls workout dvds. And post-pregnancy I'd recommend strengthening your core first as it really takes a pounding those 9 months! Search youtube for post pregnancy core workouts and do those once a day for a week or so before moving on to harder things.
Finally I'd recommend trying "raspberry ketone" supplements. I got some from amazon. I find they really help making me feel more energised and stops the hunger pangs (I gave up snacking easily after taking these).
Oh, and try and fill your week up with activities. Even if it's just a walk. Its so easy to eat out of boredom when you're cooped up at home.
Don't give up, it's very slow going after you've turned 30 but you can do it!
I hope that helps x