22 year old woman. colon cancer possibility?

Im a 22 year old woman and for the past few weeks, i have had a horrible scare about colon cancer. I've had very irregular bowl movements. One day I may be constipated and another i may have diarrhea. I sometimes have a pain in my anus. For instance, when i squeeze my buttchecks together, i feel a sharp pain. The pain doesn't necessarly hurt, but is more like a pinch like feeling. I haven't noticed any sort of blood in my bowel movement, but one a few occasions, i have noticed some clear mucus. Also, i have noticed that some of the skin around my anus is somewhat "loose" (not sure if thats the right word to use). Im guessing that can be the result of a previous hemmorrhoid? not sure..
My grandfather was diagnosed and treated for colon cancer a few years ago. He was in his late 70's when he was diagnosed. The doctor didnt mention anything about the hereditary colon cancer (FAP).  
I'm scared. I don't really know what to do? Should i go for a colonoscopy?
any feedback will be veryyy appreciated. thanks in advance for the help

[mammo]

This sounds like IBS aternating between diarrhea and constipation.  The constipation may have caused a fissure (small tear) in the anus causing pain. But to put your mind at ease, see a Gastroenterologist for an evaluation.  Colon cancer is extremely rare in people your age, so that's a plus and you really don't have the symptoms.  The fact that your grandfather was 70 before he died of colon cancer is pretty typical, and just make sure you start getting your scopes at 50 like we are all told to do. I truly dsn't feel this is anything serious, but seeing a GI doctor will help you learn exactly what is going on, get treament if needed (IBS can be controlled by medication) and give you peace of mind.  FAP is in our family, so trust that it's not in yours.  I wish you all the best, and let us know what you find out. Take care!