Muscle pain and tiredness so I quit workout

How often do you workout and what kind of calorie deficit are you maintaining?

I would suggest focusing on diet rather than exercise. If your goal is to lose weight, exercise which leaves you needing to eat more calories than you burned is self defeating. Get the food side right for you first. Once you have that sorted and a calories deficit established, then start to think about exercise, building it up slowly.

I have no knowledge about your medical condition but perhaps you should also see your doctor about the lethargy.

How much sleep do you get with an 11-month-old? Trying to cut your calories so low, with little sleep, is going to make you feel tired. I can't function on less than 8 hours per night, 9 is better!

I would do some strength training, in addition to cardio, especially for your upper back and core, starting out gently, and using very strict form. I always hurt in the neck, shoulders and back if I stop strength training. The very best exercise I've found is the hollow body hold. Going to the doctor is a good idea, of course. Exercise is even more important for women with PCOS.

First of all, cut yourself some slack. This is a lifestyle change & you're not going to be perfect at everything going all at once. Sounds like 1200 calories is just too low. Slow and steady is better than crashing, burning & no progress at all.

What is your weight loss set at on MFP? Dunno how tall you are, but 143 is a fairly low weight if you're average in height. So you should definitely be set at 1lb a week, if not .5lb. That'll give you more calories to eat & get you off the deprive, binge cycles.

As far as workouts, just ease in. it will take time for your body to adjust to new activity. You mentioned yoga. Are you going to live class or doing videos? If you're interested in videos, check out the channel Yoga With Adriene on YouTube. She's great for beginners & many of her vids are short, so it's nice when you're feeling tired or short on time. It's ok to take breaks or just do part of a workout. You have plenty of time the build up your strength and stamina.

And remember that all of this takes time. You may not see changes in the scale IMMEDIATELY. And don't let the scale be your only metric of change! Take measurements with a tape measure too. Sometimes your measurements are shrinking while the scale is staying steady. Pay attention to how eating differently & moving more makes you feel. Do you feel happier? More energized? More at peace? Remember that the number on the scale is not the be-all, end-all of health.

Cut yourself slack, have patience.