Hello. I am sorry to hear that our boy is not going in the litter box. My name is ***** ***** I have been a veterinary nurse for 27 years. I would be happy to help.
The most common cause for this to start is a urinary tract infection or urinary crystals. When ever there is pain with urination a cat will often associate that with the litter box and will seek out either cool surfaces like tile or soft surfaces like carpet as a way to prevent pain.
Male cats can easily become blocked( unable to urinate) due to infection or crystals so it really is a must to rule this out with a male cat. Some males will develop general inflammation that has no real cause. This too can lead to a urinary blockage.
Other possible causes for this could be stress, territory marking, diabetes and kidney disease. If he is eating and drinking normally and there has bee no weight loss then I would not suspect diabetes or kidney disease but since these are common problems in cats I can not rule this out.
Even though he was seen by the vet two months ago since this after I have to suggest having him seen and having his urine tested. If the test is negative then we can treat this as a behavioral issue and try a few things.
I would clean all the areas that he has urinated with an enzyme based cleaner such as Urine off. If we do not clean the area with an enzyme cleaner they can still smell the urine and may continue to use that area.
I hope this helps give you some direction. Please reply back if you have additional questions and I will be more then happy to continue. If you have no additional questions please take a few moments to provide a rating so that I am compensated by justanswer for assisting you this evening