Did you replace the nozzle and heat break when you switched from ABS to PLA?
Sounds like crappy filament; Curious Aardvark is absolutely right that good quality filament is important.
You're at the point where you likely will end up replacing the heat break (or the PTFE tubing). Nozzles are cheap; replace that for sure. Then go to a better grade of filament.
I personally have never tried the stuff coming from China; I use only U.S.A. -made, and have NO issues.

Wes