Your boy most likely has a bladder infection. If he is vomiting, straining, not able to expel ample amounts of urine, straining in the litter box then he should be evaluated by a veterinarian right away as male cats are at an increased risk of becoming blocked and unable to pass urine. When this occurs it is a life threatening issue. If he is passing urine fairly well then he should visit his vet first thing in the morning for a urinalysis. If infection is present (most likely) then he will be started on antibiotics and possibly a special diet if crystals are found in the urine. This diet may need to be fed for life to prevent recurring issues.
Please let me know if further assistance is needed.
Theresa
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