I am sorry to hear you are worried about Seus. My name is Rebecca. I am a veterinarian and will do my best to help.
Is he straining to defecate, pushing but nothing coming out? Or is some blood or mucus passing out of his rectum?
How long has he been like this?
If he has an obstruction in his colon causing him to strain, and vomit, it may be able to pass with an enema but in some cases we have to actually reach inside to remove or break down the obstruction manually. There are no safe enemas in pharmacies that are safe to use in dogs, not even ones for infants. We use Pet Enema (Active ingredient is DSS) or warm soapy water.
Sometimes dogs have severe colitis, inflammation and swelling of the lining of the colon that can look exactly like constipation except that the colon is empty and only sometimes some blood, liquid or mucus will pass. It is dangerous to give an enema to a dog with this condition.
If he is vomiting because of the constipation he needs an enema or to manually remove the bones or whatever is causing a blockage in his colon. Or, he could have an intestinal infection causing colitis and vomiting.
The best thing is to have him examined by a veterinarian, including an internal rectal exam, to see if there is a blockage to remove, or if an enema may be enough.
Let me know how he is doing and what else I can answer.