What is wrong with me an will it ever get better?

I am 20 weeks pregnant and for 4 days now I have been peeing blood and it's in the toilet I can see it but there's no blood when i wipe!!! I went to hospital the day I seen blood they done a pelvic exam and baby is fine and im not dilated... They took a urine sample and I don't have any type of infection!! I went back to hospital Saturday morning with severe back pain and they emitted me and kept me till dis morning baby was fine and I wasn't dilated they done a ultrasound to look at my kidneys and I don't have any stones in there so I'm not sure what is wrong when I pee it feels like I can't get all the urine out and sometimes it still has blood in it they told me it was prob a stone but that It had already passed but i don't understand y I still can't get all of my urine out I'm confused I wanna know what is wrong with me!!! I know the baby is ok bc they told me heart beats great I'm not dilated I feel baby moving I'm just so scared its something serious any help or advice will be greatly appreciated thank you