Is it itchy or just sore? Were you exposed to any plants, insects, pets, or anything you may be allergic to? Do you suspect that this is a bite? The yellow in the middle makes me wonder if this is pus or an infection?
Please know that I am not a doctor.
If you are concerned about this lump and blisters you need to see your doctor. There is no way, unfortunately, that we can tell you what this is on the Internet.
Let us know what your doctor says. Thank you for your question.