Re: milk blister?
A milk blister is fluid filled. Does it look like that? Mine were never yellow but clear looking.
Read about milk blisters here.
My personal experience is they are very painful and I personally have to lance mine. I steralize a needle and pop/drain it. Then I apply a small dab of neosporin and it heals very quickly. Also for me the pain was a lot less after popping it.
Just make sure you continue to nurse on that side. You don't have to wipe off the neosporin either as long as you use a small amount.
Good luck, they are no fun!