Sound like the roller isn't picking up enough paint. Plus you could condition the paint for better flow and easier rolling. Use Floetrol latex paint additive for water based paint and Penetrol for oil based paints.
When rolling try working a 3x3ft or 4x4ft area. This could get the paint on a bit thicker and give you some time to smooth it out.
Probably just conditioning the paint will solve your problem. Some paints are just very sticky and difficult to use.