You are right that no frost on the roof and the others do means you have a big time heat loss in the attic. You will also notice that snow will melt on yours and not on others and also since the roof above your eaves freezes, then you can have icedamming. Steve has done a good job of covering everything. I'd suggest laying kraft paper faced insulation (paper towards ceiling) to the depth of the joist between the joists. Basically sweep back the loose stuff, put down the fiberglass in sections, and then cover over the fiberglass with the loose stuff. Make sure you don't block air flow through any vents in the eaves if you have them.
Plastic on windows tells me you have a bigtime window leakage which may mean new windows along with insulating and caulking the gaps around the windows. Heat rises so your most effective way to stop heat loss is to start with the roof first.