Stuck in a rut after pregnancy...Suggestions and thoughts?

Hello! After having a baby in early January, I've lost about 25 lbs. At my highest with pregnancy..I was 240 (I gained about 40lbs during) and now at 5 months, I'm currently 220. I was going back to eating a strict diet of 1200 cals (I was eating healthy during the pregnancy, and gained the majority of weight towards the end) until I was cleared to exercise again, where I lost 12lbs. Now, it seems either my metabolism has been shot or I need to rev up my workouts. I still try to stick to my 1200 cal diet, but don't know if I should consider myself 'Lightly active' instead of 'sedentary' since I'm a stay at home mom (I was a at a desk-job prior). I usually do half hour workouts 5-6 days a week; with 30 mins of interval walking with an incline on the treadmill and 10 mins of push ups, sit ups, squats, and mountain climbers per day mixed in as well. I was going down a 1lb a week for a few weeks and all of the sudden I gained it all back...not too sure why but it's so frustrating haha that I've been doing what I have been doing and nothing is coming off! I drink a moderate amount of water (the only thing I do drink besides the occasional coffee to keep me awake/sane) and plenty of protein by eating chicken almost everyday for lunch and dinner. Any suggestions as to see a steady weight-loss and any in-put from others who have been in this same position would be helpful as well!
Sidenote: I'm looking to at least lose 40 lbs in a respectable amount of time. Definitely not right away as I would of wanted pre-baby but you know...it'd be nice to see it gone by the end of the year.

Thank you in advance!