If so how much or how much would you consider normal before starting to worry?

DS has been in the same clothing forever and lately they look really loose. I weighed him today (him naked and subtracted from my weight so not 100% accurate) and it appears he has lost ~12 oz in 1 month...it has been just over a month since he self weaned. He also had a really bad allergic reaction to yeast just after we weaned. He still gets breastmilk from my freezer stash, but not as much as when he was nursing, and EO28 Splash, which he was also getting while breastfeeding. I was going to wait until his 2 year well visit in April, but now that I realize how much, how fast, I'm a little more worried. While still nursing he was gaining weight, but at a slower rate, with just over 1 lb from 18-21 months. Anyone else experience this?

(I wasn't sure if this should go in breastfeeding or toddler)