hope he is feeling better soon.

If you are worried/concerned I would take him to the dr. I took DD when she had a cold (only had a runny/blocked nose though, no green snot) as her cough sounded a bit nasty. The dr said she was ok and just give it time, I felt a bit silly after but it did put my mind at ease.

Maybe take a trip to the chemist and see what the pharmacist recommends?