I recently stretched my ears from 2g to 0g.There wasn't any pain, but after stretching my ears, I start to feel throbbing and it was hurting a lot. So I took it out today and clean it, I notice theres blood. Is that a blow out or tearing? And how should I treat it? 

I would guess that it's tearing as opposed to a blow out.  I would downsize (like to a 4g) and SSS and baby them for six months.

 I agree. If you want to be super safe, you could remove the jewelry altogether and give your ears a total break.  Also, the sea salt soaks only need to be done while you still have an open wound. After your ears are superficially "healed" (ie not raw), you can massage the tissue to help break down any accumulated scar tissue. 

 take them out and wait a least 6 monthsto stretch again. and when you are realy try going to 1g first. 2g to 0g is usually a very hard stretch.

 without a doubt downsize for a bit.