What does it mean penls glans & just behind it are painful?

FromBanalToBalanitis: It means it might have an infection. Is it red and swollen? That's called "balanitis." And if you are also uncircumcised and it is inflamed it's called "balanoposthitis" (try and say that with a mouth full of graham crackers!). If there's blisters there that's another red flag, so get it checked-out by a doctor for that and to make sure something else isn't lurking in or around that area.