I think I might be a weirdo with this, but it sounds COMPLETELY normal to me. He doesn't sound at all delayed. I think boys tend to be on the slower side when it comes to speech and I know SO many children (especially boys) who are labeled as being slightly delayed and then in the end, they catch up by 3 yrs old and are just fine. It doesn't seem delayed to me when so many children are like that. Anyway, so my opinion is to not worry about it. He sounds like he's doing great.
But that all being said, you are the mom and only YOU know what is right for your child. If you're worried, there is definitely no harm in speech therapy and no harm in doing whatever the doctor suggests. I think out of all of this, it's most important to follow any feeling you have on it.
I do tend to under-worry things, so keep that in mind with everything I've written!
Oh, and I wanted to add something really quick. Children have brain leaps where literally one day they can't do something, and then over the process of about 2-3 days, their brain develops a little more and suddenly they are able to do something they couldn't before. I would bet you this is the case with the speech. He's probably been busy doing other things and hasn't been as focused on developing his speech. And I know I said this tends to happen more to little boys, but it also happens to little girls sometimes too. There is such a HUGE difference on what is normal...and I'm a slow believer in children being delayed unless there is something significant to prove it. Otherwise I think they are just developing different areas at different speeds. Meaning, he might be more focused on social skills or physical skills than on verbal communication right now. My nephew could hardly speak until he was three years old. Now he's eight and he speaks great. I've met several other little boys (can't think of any girls that took that long to speak, though I'm sure they are out there) like that. I think they all develop differently...anyway, enough of my rambling!
Just kidding, I keep thinking of more to add (after I read other responses). You mentioned that he used to say some things that he no longer says. I wouldnt' worry about that at all. My daughter (5 yrs) and son (14 months) are both that way. It was in every way they developed almost. My daughter rolled over once and then didn't do it again until a month later. She started walking and then didn't do it again until a month or two later, etc. My son is doing the same thing. There are words he used to say that he is no longer saying. I know he can say them, but it's like he tries it out and then sits and thinks about it. Same with how my daughter was. I've heard of lots of kids doing stuff like that. Anyway, just wanted to say that sounds normal to me too. Okay, I'm really done this time!