Hello. I think I can give you some answers from my experience. I have low thyroid function and I'm older and am on bio-identical female hormone replacement that is compounded by a pharmacy. I've been through adjusting different levels and testing of female and thyroid hormones to get the right balance. The symptoms you describe are what happens when they are out of balance. Progesterone in excess does cause sudden weight gain. That happened to me when my doc cut the estrogen in half resulting in more progesterone dominance. They have to be balanced against each other because these are the hormones involved during menstrual cycles and pregnancy. The weight gain with excess progesterone is what happens in pregnancy. Having low thyroid hormone levels cause thinning hair and weight gain too. I have thinner hair too, but at some point with age, it doesn't seem to come back full like when I was younger after balancing hormones. Having a low T3 suggests low thyroid levels. Your body needs sufficient thyroid hormones for metabolism. If it's too low, you're exhausted and just don't have enough gas in the tank to run your body with the energy it needs. I take Naturethroid which is desiccated pig thyroid and has both T3 and T4 (Thyroid stimulating hormone) in it. I think the synthetic version doesn't have it all, but one of them is the precursor to the other. The doctor who manages this for me is an environmental medicine doctor. Integrated medicine might look at this too. I think your birth control pill might have added enough progesterone to your mix to become dominant and forced the weight gain. The risk factors for the implant you have does mention side effects for irregular periods and spotting, and the added birth control pill was probably to trying to counteract that, but at whatever dose it is. This all needs to be carefully balanced somehow and you should be able to control your weight if it is correct. You'll need to decide if this implant is right for you and ask if everything else can be adjusted to accommodate it. I would recommend talking with a compounding pharmacy as they will know a group of doctors who prescribe this for their patients. Mine is a mail order pharmacy, but there are also local pharmacies that do this. Here is my pharmacy's website. http://rvcrx.com/