In the photo it looks like a superficial wound with signs of healing around the edges and, maybe, a mild infection vs open area, in one area.
It does not look like an abscess.....
Of course, the best way to know what is going on would be to have your GP take a look at it in person.
Just throwing a random oral antibiotic, without even obtaining a culture to ID any possible infection, is not the way to fix this thing........
So. What should you do?
Stop trying to treat this on your own, especially since you are concerned it is not healing well.
Get into see your GP soon for a good exam and, if indicated, the correct antibiotic..
If you can not get into see your GP for some reason then you may want to head on over to the A&E for a correct diagnosis and treatment
Does this make sense to you?
I realize that this was not the answer you were hoping to hear but it would be unfair to you and unprofessional of me were I provide you with anything less than truthful and honest information.
Surely, you prefer that I tell the truth rather than what you wish to hear. Because it reflects very poorly on me unless you press one of the top three feedback choices, keep this in mind when rating my answer and please do not punish me for being honest. I understand that this may not be easy to hear, and I empathize.
Dr. Rick MD FACS