I'm not too knowing about the female body, Google doesn't know, my girlfriend doesn't know.
We will be having sex, there will be lots of squirting (several fluid cups) and either her vaginal is swelling up and rejecting me, or I don't know. Because I'll have just the head in, and she swears it feels like it's all the way in. On my end it feels like it is literally velvet jello pushing me out of her, once during a powerful squirt, I was pushed all the way out.
Any clue what gives?
Have a look at the condition vaginismus, and see if it matches your experience.
As for the fluid, that's quite unusual. My first guess would be urination, but it could be a cyst or even indicative of pregnancy.
I don't know enough about your situation to suggest what is most likely, but does she have any pain/physical signs down there? Redness? Lumps?
Worth a visit to a doctor.
No clue. I've never been entirely pushed out, and it wasn't related to an unusual amount of juices, but it's happened a few times that women tightened really hard during sex and I couldn't move without pain/discomfort to both me and them. Getting out and waiting a bit while trying to make them feel more relaxed helped. Sure, I've had trouble getting in plenty of times especially if we didn't have enough patience for foreplay, but I think what you are describing is different since it happens out of nowhere after sex already started.