I don't know what it is...

[Sassy_luvr]

It is not puss. It is just scabs. O.K., if you trip and fall and it starts to bleed then when it stops bleeding there will be a scab right? Well if it itches and you scratch the scab off it starts to bleed right? Well that's how Sassy's are. They are mainly located on the back of her neck. There is about 13 of them on her neck, but only about 3 on her back, and just 2 where her tail is.

[Kymcole25]

What size are they?

[Scooby4]

These could be old flea or tick bites. They heal up and itch again. The dog then scratches them till they bleed. Scabs usually itch when ready to fall off.
If you have a flea collar take it off temporarily. This could be irratating the area. Get a dog CONE collar. Those ones that wrap around the dog's face. This should help the dog from chewing on the back area till the scabs heal. You can find a over the counter spray for antibacterial/hydrocordisone spray at a pet store to apply. You may have to shave the area for good access and adherence.
I also suggest giving a dosage of Benadryl to decrease the itching. The dose does matter for weight. My dog weighs about 30 lbs and can take 1 4-6 hour benadryl tablet safely.
There are shampoos for this. Avoid the flea and Tick kind because they can be quite harsh. Use Frontline or Adam's flea spray (OTC). Only if you see fleas. Try finding a shampoo for sensitive skin and only wash once a week or follow directions. Too much cleaning may not be beneficial.
Hope this helps. You may ask about other "Hot Spot" treatments at your local pet store. This would be items that would help make the dog NOT want to continously bite, scratch or chew in this area.