Not sure about what to use with dimetapp. Check with a chemist or Dr, but usually panadol is ok with most things. I often use neurofen and panadol together.
ALso a good thing for colds is fess nose drops (comes with a sucker thing to clear nose)! And we love our vapouriser here!
Good luck and hopefully colds stay away from you! We've just come through a bout of gastro, just hoping the rest of the fam doesn't get it. I just hate any kind of illnesses, not fun. xoxo