Inflammation of colon and belly fat on left side what could it be?

Many things. Diverticulitis leaps to mind, although you are young for it. Also hernia, trauma, associated skin infection, tick-bite or other insect, skin rash from chemicals and a myriad other possible causes! See your doctor to figure it out!
Unknown. There are a number of causes for inflammation of the colon. Common causes include diverticulitis and bacterial or viral infections. A careful history and physical exam, along with reviewing any diagnostic studies needs to be done. You certainly should seek out a trusted physician to get your answer.
(L) abdomen inflamed. Do you eat many nuts or a lot of popcorn or things with tiny seeds? Do you have a history of diverticulosis or rectal bleeding when you eat the things mentioned above? Any change in bms? Any history of trauma to left abdomen? See fp for evaluation, imaging &/or testing if necessary, treatment.