Little bump under the eye

One of my rats is having a bump (I don't know if that's the right word) under his eye. He doesn't seen to be bothered by it and he's not having any other symptoms. I saw this bump at least three weeks ago. There were days that it grew just a bit and it came back the way it was before, but there was no big change since I saw the bump for the first time. What can it be and what can I do for him?

Just for the record: I didn't take him to the vet because two of my other rats were really sick at the time and I couldn't afford taking three rats to the vet at the same time. One of them unfortunately had to be PTS and the other is still sick, so taking him to the vet now would be hard.
Besides, I didn't think it was worth it exposing him to all the stress involved if the bump wasn't bothering him and it didn't have any change.
P.S.: I'm trying to post two pictures of him here, just don't know if it's going to work.

I can't see it very well, but it may be an abscess or a cyst or may have a tumour associated with an abscess.

Facial abscesses are extremely serious and often terminal.
I would suggest strong antibiotics that will penetrate well (clavamox is good but metronidazole etc may be needed).
Can you smell an abscess/pus?
Is there any wound etc on the inside of his mouth?
Keep a close eye on it to see if it gets larger.

A vet will be able to tell if bone is involved (I just had to have my baby boy pts because of bone cancer that presented as a facial bump near his eye) ...... and the vet may need to do an xray to see if it is bone cancer or bone infection (both reasons to humanely pts immediately), if there is tooth involvement, or if it is an abscess.

http://ratguide.com/health/integumentary_skin/cysts.php
http://ratguide.com/health/integumentary_skin/abscess.php
http://ratguide.com/health/neoplasia/sarcoma.php

Info on having a rat pts humanely because most vets do not know how so owners must make sure it is done right and stay with their pet if at all possible http://www.ratshackforum.com/forum/showthread.php?t=7652

Some people are using CBD oil to treat various diseases in rats and report success but I have no knowledge of types of treatments or dosages

I hope it is a simple cyst or an easily dealt with abscess
I hope this info helps
Good luck