I've hit a plateau... I'm stuck

For the past year, I've struggled a lot to lose the 33 pounds I've lost. 3 months ago, I managed to get down to 6 pounds away from my pre-pregnancy weight, but I haven't seemed able to drop even a single ounce since, no matter what I try. I first changed my eating habits at the beginning of my weight loss journey, and continued to tweak them along the way. I cut all beverages from my diet, besides water and sun tea. I began exercising(cardio)1-3 times a week for half an hour each and have since built up to (cardio+strength training)3-5 times a week each lasting between 30-60 minutes. I've been trying to avoid weight loss supplements/diet pills, but I'm starting to think that it will be impossible to pass this plateau without them. I average 7 hours of sleep and 1,200 calories. I'm 5'1, 19 years old, and currently 147 pounds. My short term goal is 140, while my long term goal is 115-120. Any suggestions..?