My 2 1/2 year old is always saying he's sick...I always wonder if he really isn't feeling well or likes to say it...I don't know. But also has no symptoms, so I'm leaning towards it being a phase. But I would keep an eye on him, how he's eating, pooping, playing normal, etc.
The one thing I wanted to tell you about growing pains...My 5 year old was crying a lot around dinner time or when he'd go to bed saying his knees hurt, or his legs hurt so bad. I did a search for growing pains because I kept thinking it must be that...anyway, almost everything I found said that growing does not hurt and we label a lot of unknown pains as growing pains. But as far as my son I know he is SO active...he rides his bike through the park for hours at a time and from what I read it could just be straining muscles or overexertion or something. Anyway, all this to say, if he keeps complaining and you sense something is wrong, go get it checked.
Hopefully it's just a phase or something.
All the best!