Swelling gum means you have gum problem or what we call gingivitis...
poor oral hygiene cause gingivitis, but in your case, if the crown was bad, like overhanged or undersized there would be a problem, cause this crown may harbor bacteria in the gingival line (gum line) which cause inflammation of the gingiva (gum).
The treatment for your case may be replacement of the crown plus proper oral hygiene...
Your English is just fine. You need to go to the dentist!!!! Infections spread rapidly in the mouth!!! Do you mean an abscess or a tumor. Abscess if you don't know is usually an infection under the tooth in the roots. I know it can be expensive but you shouldn't be in this discomfort! They use different antibiotics for different infections. I do wonder why you didn't go back before this! Dental pain can be so bad.
Take care.