I think my male dog is in heat.. or something else :[ help?

He isn't in heat.

Is sleeping a lot out of the ordinary for him? Does he seem lethargic? Most dogs sleep a lot during the day at home. However, if he seems to have no energy at all & isn't acting like himself that could be a sign of something more serious going on.

By "not eating" do you mean he wont eat at all & hasn't for several days? Has he been throwing up as well?

When he urinated on you was that the only time his behavior was out of the ordinary? Is he urinating more often? That would be a cause for concern.

Humping is really no cause for concern, just an annoying habit.

Any of the things you listed could be nothing to worry about, but could also be signs that something more is wrong & yes, at that point a Vet would be my suggestion. Most of this depends on what is normal for your dog & how is behavior generally is. If he really seems to be out of sorts please get him checked out. There is nothing any one on the internet can do to help a sick dog.

One two to add to Ladystans list...Is there a female dog in your home or near your home that is not fixed that may be in heat?

And is your dog neutered?

since male dogs don't go into heat. doubt it

what breed?

what age?

when did he start doing this?

how much training has he had?

does he have problems with pottying?

have you changed his food?

do you feed table food?

has anything in house changed?

have you got another pet?

is there a new baby in house?

have you moved recently?

He should be neutered, but of course, that requires a vet