It depends greatly on your weight, Redaria. Are you an Irish land whale or a German walking strudel? Most Chinese women are thin, so it's not sure you can find good clothin that would fit you...

There are some shops that sell clothing for mythical creatures, but they are specifically targeted toward Westerners. So it won't be easy to find something affordable AND XXL.

Tell moar info about your extra pounds and I'm sure i can ask Pedro, the Mexican IT guy, to give me some addresses. His wife packs quite the xtra pounds herself!

Redaria, you should try going to Beijing Zoo Market. Just opposite the zoo you'll see a number of wholesale warehouses. Each one is crammed with stall after stall of clothes vendors. Beijing zoo is probably one of the cheapest places to buy clothes but it always gets extremely crowded and noisy here at the weekends, and you can't try on clothes. Make sure you know your clothes size before you go as there's no returning items after you've bought them. The best way to get there is taking line 4 directly to Beijing Zoo station. Go midweek if possible.