blood coming from rectum

Question
yesterday we went to the dog park. Tyson, 6 year old male boxer, had a normal bowel movement. Then trys to have another bowel movement but nothing comes out. He keeps trying, his penis evens comes out, and then some blood spurts out. He also was a little gagging last night. Some clear mucos like came up once. He seems tired and acts like he doesnt feel well.

Answer
This is a veterinary matter; it may simply be a digestive upset or illness, but generally bowel movements are sloppy immediately preceding straining and blood in those cases.  However, it may also be a blockage, perforation, or tear, which can become life-threatening.  He needs to get to the vet - far better safe than sorry.