thanks guys

Yes, slap cheek is not good for pregnant mums, but it is no longer contagious if the rash has come out. I don't think it's measles, as he hasn't had a fever, and is happy, playing, eating, drinking, etc. A reaction to antibiotics is unlikely, as he has no other symptoms, and was taking them for ten days, with no reaction.

I'm now thinking it is probably just part of a virus, as he isn't getting any worse. He has gone down for his nap, and I'm hoping the rash will have faded a bit by the time he wakes up. I think it has faded from his face a bit...it's just still quite prominent on his torso, so I'll see. I wouldn't say it's a dark red rash or anything, it is light...it's just all over his torso though, so quite noticable (well, it's just like a heat rash, really).

Anyway, thank you very much for your advice, ladies - much appreciated!