I don't know if this is supposed to happen...

I bought my first cup, a small LadyCup, last month, and this will be my first period with it.  I did a few dry runs, to try to get the hang of inserting it, and everything went great.  I have a finicky period, and spot a lot before it starts, so I've had my cup in occasionally for the last couple of days.  I haven't had any trouble inserting it or feeling it or getting it out, until today.  Normally, I could just bear down until I could reach the top of the cup and pinch it lightly to break the suction before pulling it out.  But today, I went to pinch, and I think my whole freaking cervix was inside the cup.  I've felt the bottom of my cervix resting on the cup  before when I've pulled it out, but this time, I mean the whole cup was literally just full of cervix.  I had to loop my finger around the rim to break the suction off.  I don't know if this is normal, since I've never used a cup before.  So is this normal, or is the cup suctioning my cervix down inside it, or do I just have a super fat cervix, or what?  I'm also concerned because I have an IUD, and if it's sucking my whole cervix inside, I don't want it to dislodge my IUD.