Hi T.,
I'm no expert on this subject, but I think breastfeeding actually keeps weight on you. When we went to breastfeeding class before my son was born (he's 6 months old now), the instructor, who is also an RN and lactation consultant, said that while it does help burn the calories you're currently taking in and helping to shrink your uterus size back down, it also can encourage your body to hang on to about 10 pounds of pregnancy weight. She said many people assume it keeps weight off, but not true in all cases.
In reading the books as to where all those pounds come from besides the baby, they count about 10 of those pounds as "maternal fat reserves" to ensure your milk supply is plentiful whether you eat enough or not. So it does make sense what she said. You're nursing body may be telling itself to hang on to the extra pounds for your baby's nutrition.
I personally gained almost 35 pounds during my pregnancy. A few days after I got home from the hospital, I had lost about 18 lbs of it. I only got to breastfeed for about 3 1/2 weeks for other reasons, but in the next 3 - 4 weeks after I stopped, I was only about 5 pounds away from my pre pregnancy weight, and I now weigh a little less. I also have a friend who had 4 kids, and the only one she didn't breastfeed with is when she lost weight the fastest.
Of course I'm not suggesting you stop breastfeeding. I was sad that I had to stop. Just know that if you're eating as reasonably as before you were pregnant and nothing is coming off, it could be that when you do decide to stop, it could melt away as quickly as it did on us.
I may be wrong, but I do think that's what happened with me. If not, don't worry, I'm sure you'll be back to your old self before you know it. Congrats on your new baby!