I can sympathize with you so much! I absolutely HATE it when the dentist/endodontist tells you "it looks good to me" or "i can't see anything wrong with it". I got tired of my husband telling me to just forget about my tooth pain, that it was "just a tooth, for cripes sake". I don't think anybody but yourself knows the pain you feel, and they have no right to treat you as if you are making your pain up.
I had a similar thing happen to me, but in a different order. First I had the root canal, which did ok for a year. Then it abscessed. So I dished out the $1000 for the apicoectomy. The thing still hurt! The endodontist didn't see anything wrong on the x-ray, but fortunately he believed me and offered to retreat the rootcanal for free. I figured if that didn't take care of it, or if the retreatment would have been out of my pocket, I was just going to pull the tooth.
Fortunately, the endo got in there and found parts of canals left untreated and not sealed. So he cleaned it out and resealed it. That has been over a month and so far so good.
If your abscess was down on the root, the root canal itself might have left abscess still down there. Does it feel warm, swollen, or anything like when you had the abscess? I would think it would take a lot longer to heal that way, because your body has to like reabsorb the abscess. The "good thing" about the apicoectomy is that is cuts out and removes all the infected tissue. But it is costly, takes longer to heal, and there still aren't any guarantees.
You pretty much have to decide on your own. The dentis has a duty to try and save teeth at all costs. You have to decide when and where to draw the line. The only thing I can tell you is that if it still hurts, something isn't right. If you want to try insisting that they retreat you free of charge, do it. If it wasn't a specialist that did the root canal the first time around, go to one. Mine was done poorly the first time because it was done by a dentist that didn't have the microscopes to see the canals with.
Good luck, hope I have been of some help.