How do i fix this strange problem, its making me terribly sick....?

I've got a strange problem...I have compulsion for thinking about the same thing time and again (at least every 5 minutes) throughout the day...I think about a problem which actually has a solution....Actually, i was emotionally abused (terribly) by 3 guys at high school 3.5 years ago...I fear that those guys might see me walking somewhere on the street and make fun of me (eg. my way of walking or my ridiculous expressions- coz i feel i have a ridiculous way of walking and tend to make strange and ridiculous expressions)....I have said about this to my elder brother and he has assured me that he would beat up those guys if they did that to me.....But still i keep imagining about the whole thing- as how i would be walking on the street and then see those guys at a distance imitating me or looking at me mockingly or laughing at me ...Then how i would pass them and then call my brother and get their asses kicked...I fear the humiliation i have to bear (for a few minutes) till my brother arrives at the spot to beat them up.....I don't fear if i'm ridiculed by anyone else, but i terribly fear being ridiculed by those three guys....I keep imagining this whole scenario at leat 100 times a day since past 25 days, which makes me have bad headaches throughout the day..I've become so dejected that i have lost motivation to do anything and have started considering suicide.....Could these unwanted recurring thoughts be due to OCD? Please also suggest a way to get rid of this problem...