In order to help out, I'll need to ask a few questions.
First, what kind of fiberglass are you using? Mat or cloth? If you're using mat, I would suggest switching to cloth, since mat is a bit heavy for applying to a helmet. Regardless, my ultimate suggestion would be to slush a layer of rondo on the inside of the helmet prior to applying fiberglass. This gets all the tiny crevices filled in, and will help prevent air bubbles when glassing.
Second, how are you applying your fiberglass? My method involves coating a section of the inside of the helmet with resin, placing a strip of fiberglass cloth in the wet resin, then dabbing the cloth with the same brush used to apply the resin until the resin is soaked through (adding more to the top of the fiberglass cloth if necessary). I take care to work in small sections.
Last, how are you mixing your resin? You mentioned that it was thick when applying it and not soaking through the fiberglass. You might be adding too much hardener, causing it to set up too quickly. When applying resin, it should have the consistency of warm honey (a bit thinner than honey at room temperature), and should flow pretty easily.