If it was my dog I would take him to the vet ASAP. He may have a urinary tract infection which is extremely painful. It may wax and wane but without treatment prescribed by a veterinarian (antibiotics) it will not go away and will get worse and may result in more complications. The vet may also need to do an ultrasound besides a urine test and blood work to rule out bladder stones and properly diagnose your dog. Sounds like he may have allergies too. Often there are genetic factors involved, the food may have very little to do with it. Use the search engine here to look up bladder stones, and allergies.
PS: I would just go to the emergency vet, now. Today. Urinating blood is serious and requires immediate medical attention.
