Hi L.,
I went through the same thing when my daughter was 2 weeks old. She is now 5 weeks old.
I weened her by giving her 1 ounce breastmilk and 2 ounces of formula combined. Then, as the supply got low I did 1/2 ounce breast and 1 1/2 ounce formula. By the time she was on 100% formula, she couldn't tell the difference.
Here is what I did to stop lactating and it took about 2 weeks. After I emptied my milk supply, I put a cold cabbage leaf in each of my bra cup. (it sounds weird and it smells, but it works. My ob/gyn told me to do this). After you do this bind your breasts with an ace bandage. Repeat this when the leaves wilt...a few hours. During this process I engorged so much, I had to pump once and I repeated the process. I did the cabbage for about a week and I stopped. I still leaked but my breast pads were sufficiant. Today I am free of cabbage, pumping, and leak free! I hope this helps.
Good luck,
S.