Have you gotten your breastmilk production up? I've been meaning to ask, because I know it was bothering you. I had to completely change how I breastfeed Sorsha. She nurses better when I'm standing up, and she nurses the best when I'm walking around or if I'm swaying back and forth. You might have to do something similar with Warrick.
Have you considered doing crunches? I did that every morning after I breastfed Sorsha when I was on maternity leave, and every night after I breastfed her. I started with three sets of ten each time, and by the end of my maternity leave, I was up to 200 in the morning and 200 at night. I'm a sedentary person and I had serious weight problems growing up, but I still managed to lose a lot of weight. I've gained it back though, since I went back to work.
And even if you don't lose the weight you want to by March....just remember that D doesn't love you because you fall in a certain weight category, he loves you for you. I have some insecurities about my weight, but William has been very supportive towards me, to the point where I'm somewhat comfortable with it. And before anyone says anything, William doesn't have a filter between his brain and his mouth. If he does, it's broken or out of order.
As for figuring out what to do....you need to prioritize. It's becoming clear that you cannot exercise the way you want to AND breastfeed. You need to figure out if you want to put the focus your own health (because lets be honest, excessive weight IS unhealthy) and thus stop breastfeeding so you can exercise the way you want to, or if you want to put the focus on Warrick's health, which would most likely involve less exercise and continue to breastfeed. It's not about putting you first or him first, because whichever choice you make is the right choice. It's about choosing your priorities. There are immediate pros and cons to each choice, as well as long-term pros and cons. Of those two choices, both the short term AND long term pros outweigh the cons.
And whichever choice you make, DON'T FEEL GUILTY. Neither choice will make you a bad mother.