My son is experiencing lower mid abdomen pain. He cannot pass gas and says that his mid back also hurts to the touch. He has nausea and has not eaten all day today. No fever and has not had a bowel movement since Friday, before Friday last movement was Tuesday. Friday's movement he says looked like it had blood in it as if he had eaten red peppers. He has not eaten any red peppers that we can think of. Also, in the past he has had what looks like a almost whitish mucus like in his bowels.

How old is he? Has a doctor seen him yet about this?

No he just came home from a friend's house and told me about it today. He is 16

Are these new symptoms? Or has he had them before but didn't say anything?

Yes they are new. He has been seen for the funky mucus like in his bowels but it has never happened while we were at the doctors. He doesn't say much till it has happened.

Save a stool sample (small) in a clean container before he sees the doctor, if he can move his bowels in time.
Blood in the bowel can range from non serious (hemorrhoids) to serious. Mucous isn't uncommon, but again, only tests and an exam will provide answers.
Ask him if there is anything he eats out of the ordinary - people who swallow gum on a regular basis have often had all the gum stay undigested in the bowel and cause serious obstruction.