Think about it for a second - the primary difference between the part of the face where you can shave and the part where you can't is in two factors

1) There is more curvature and your hand is more awkward holding the razor when you shave your jaw/neck than your cheeks/sideburns

2) The hair could be different in both places

While (2) is possible it's less likely to have dramatic variation which can explain the difference you are experiencing, so as the two australians above noted the most likely reason is (1).

The usual recommendation is to start with the easy part of your face, using your usual method for the rest, and gradually expand it. This way you can tackle one small area you have problem with at a time until you figure out how to shave it well.

You need to strop between shaves, there is no way around it. If you do not strop your razor the edge will oxidize faster than a normal cartridge or DE blade and in few more shaves it will need honing again. Everybody has done it, so while it's very important it's not some sort of magic and you're more than capable to do it.
If you have difficulty stopping on a hanging strop at this point you can put it along the edge of a table/counter and then you don't have to worry about keeping it taught.

You probably notice a pattern to my suggestions - break down things into separate pieces and concentrate on one piece at a time.