Hi Chiara
Your dentist will be the best option to confirm whether an abscess and if it is, at least you'll know and be told how it can be treated.
I'm off to Malta tomorrow for a working holiday with the family and had a toothache since yesterday, so went this afternoon to my dentist and apparently chipped a tooth at the back, probably munching on a Subway lunch and fixed now......which is a relief.
I would definitely visit your dentist to find out what's going on. Good luck, Chiara x