Kitten problems, Please help!

I have never had a problem with raising kittens before. I've raised 4 week old feral abandoned kittens, rejected kittens, and even a kitten that was given to me too early. I thought I had every kitten problem figured out UNTIL I picked up two female litter mates a week go. They're about 8 weeks old and they are spazmodic as ever! One in particular, Sierra(aka Miss Thang for her attitude) seems to have a litter box problem. She uses the litter box during the day, in the middle of the night, but not in the early morning! I've notice between 6am-7am she will pee on the bed! On my side!
I clean the litter box every night when I get home from school and the food bowl is on the other side of the room. They both sleep with me above my head. Has anyone had this problem before? Please help, I'm getting tired of rolling over into little suprises!

 

you should rule out any health problems like a UTI. Do you suppose she's just so comfy she is not willing to leave you to go potty?

 

I was thinking that maybe that was the problem, but I was playing with the other kitten this morning and I see Sierra come up from under the dresser, and jump right on the bed and squat down to go! Is she just being defiant or what? I gave her a good flick to the side of the head and she ran off.
Well, looks like my next paycheck is going into a vet appointment! If anyone has any advice or tips to break her of this habit before then, please post!

 

Just curious as I dont know too much about cat behaviour but I was wondering if you have a litter box for each cat?

 

My cat Miss Brina only pees on the bed when she has a UTI/crystal flare up. And you can see a tinge of blood by that point. Definately rule that out first. Her problem always seems to happen after vet hours too, so I usually quarantine her to the guest room with two litter boxes, and a plastic cover on the bed. So there's no where soft for her to go.