Getting it to stay?

I've been reading about cups, but haven't been able to find them locally. The moment I saw something called Instead offered at wallmart, I was excited. I had to try it. But I ran into the same trouble I ran into with tampons. The darn thing won't stay!

Okay it does go in better than a tampon. The first time inserting hurt like hell, but after that at least it went in. Tampons don't come anywhere close.
How far do I have to push the instead in? I tried to go until I could feel pressure behind it and couldn't go further. I even just barely got the rim past the pubic bone area. Even so, I could not stop feeling the instead, and if I sat down, out it came, causing major discomfort. I can never seem to get more than a couple hours of wearing before having to take it back out. More often than not, I'd have to keep pushing it back in every few steps or so. Obviously I'm doing something wrong, or this just isn't working. I don't like the thought of being stuck on pads for the rest of my life. Plus my flow is always heavy and I'm tired of leaks.

It's meant to sit behind your public bone, sort of held in place by it, along the top wall of your vagina. You should be able to feel your cervix though the cup part, and it shouldn't be blocking your vagina at all. I haven't managed to get one to sit right (I suspect I'm too short up there), so let me know if you work it out.

Insteads are quite different to other cups though. 'Normal' cups sit sort of perpindicular to what an instead does.