Lumps near dogs penis?

My Lachon (Lhasa Apso X Bichon Frise) turned 4 in March. He was originally brought from a pet shop (it's pretty much a puppy mill pet shop). However we rescued him when he was 18 months old. His previous owners didn't want him anymore. He is desexed but only got desexed when he was around 18 months, just before we got him.

A couple of months ago maybe April or May we got home and he had a big lump about the size of a golf ball maybe a little smaller, it was not near the tip of his penis it was about halfway in between the tip and where his balls would be. The lump was hard. About 10 minutes later it disappeared. We though maybe it was something to do with needing to pee. He didn't get the lump come up again until maybe June.

Then again on Wednesday, the lump on Wednesday was especially hard but around the same size as the previous lumps. When they come up I usually let him out in the backyard to go to the toilet and watch him carefully, usually by the time he comes back in, whether he's pee'd or not, the lump has gone.

Now today he has another lump, the lump we've seen before is not there, it's a smaller lump nearer to the tip of the penis today. It's not as hard as usual.

I think I'm going to take him to the vet for an examination but I just wanted to know if anyone knows what this is or could be? He is in great health, he gets exercised daily and fed well. We've only ever seen him have his red thing out like once or twice he doesn't get it out much if that matters haha.

Thanks in advance for any help, please no rude comments/answers. The dog will go to a vet I just thought it would be a good idea to put a question out on here.