Hi Andreea and welcome
Im so sorry to hear about your little hammy. I found some info searching the web.. I hope your little guy gets better soon. Good luck
This ones a pretty good site...
http://www.hamsterific.com/IllnessGuide.cfm
http://www.ahc.umn.edu/rar/MNAALAS/Hamsters.html
Abscesses of one or both cheek pouches are also very common among pet hamsters. These commonly result from penetrating wounds to the lining of the pouch caused by harsh foods or bedding materials. It may be very difficult for you to know whether a swelling in the area of the cheek pouch is an abscess or simply food or bedding being temporarily stored within the pouch. Generally speaking, the swelling resulting from a cheek pouch abscess persists, but a pouch swelling from stored food or bedding disappears when the animal empties its cheek pouch.
If an abscess is detected or suspected, the abscess must be opened and the pus drained or removed by veterinarian. An appropriate antibiotic also will be prescribed. Furthermore, the underlying cause(s) for he abscess must be eliminated, if possible.
http://exoticpets.about.com/cs/hamst...sterhealth.htm
Abscesses: these are pockets of infection, which can form from fairly minor breaks in the skin. Pus accumulates under the skin, sometimes forming a sizable lump (which may sometimes begin draining on its own). Abscesses can form from cuts or scratches on the skin and also in the cheek pouches if abrasive food material causes scratches in the lining. If a hamster continually looks like it has food in packed in its cheek pouches, there may be an abscess or an impacted cheek pouch present. Abscesses require veterinary attention for draining, flushing, and treatment with antibiotics.