What should I do?

My boyfriend and I have a 9 month old daughter together, we are in love and together..

Anyway, I found out a few months after having my daughter that I have a thyroid disease.. it makes me extremely tired, and foggy headed and honestly depressed sometimes. I'm taking medication for it but I'm on such a low dose because I'm breastfeeding and it can be passed through the milk. My medication dosage needs to be altered to a higher dosage the DR says because after running more blood work after being on the medication for a few months it's not helping very much. I still feel lethargic, like I'm just going through the motions. Some days are better than others. But still I never feel normal.

So today I told him when I go back to the doctor in a couple months I want to stop breastfeeding. That way I can get on the right dosage and start feeling normal again. The baby will be about 11 months. Eating a little more solid foods and a month shy of being able to drink regular milk.

My boyfriend didn't like my idea, and thinks I should wait until she's 12 months and then wean her off gradually. And if I do what I want he will have major attitude about it.

My thing is, the baby is perfectly healthy and thriving, and when I stop breastfeeding she's still going to be great.. but I'm not ok. I literally have to push myself everyday just to do the simplest things. I thought I had PPD but I think it's just the thyroid.

So what do you guys think????

Any feedback is appreciated...

Also I feel like, who is he to tell me what I need to do with my body. I know what's best for me, right? He's not a damn woman.. or a mother. I take care of the baby mostly.