Tips for creating a seal?

So I've dabbled in menstrual cup usage a few times. The first time I used it it seemed to work perfectly, but the second time and every time since it seems to be a struggle - almost more than its worth.

The biggest problem I seem to be having is getting the cup to open and create a sea inside me. Not to mention all the strain put on my already sensitive lower back while repeatedly inserting and removing it to try to get it to pop open and seal.

After inserting I attempt to rotate it like instructed which is supposed to make it pop open, but I can't really seem to get it to rotate and upon inspection (running finger around edges) it's very often not unfolded all the way, let alone created a seal.

It has gotten to the point that I've just gone back to pads and tampons- but I really like the idea of cups, if only I could get it to work!