very dark urine with large particles

for 3 weeks i've had abnormal urine, and from the second week to now having tons of tiny little particles floating around in it. this morning my urine was so dark it was orange/brown. and later i had urine with LARGE particles in it, in addition to the normal small ones. these large ones looked sort of like thin skin, only more flexible, and they were really white.

also, i have abdominal pain that comes and goes, and today i've had lower back pain that comes and goes. i don't know if this is related, but i've also had terrible headaches for the last 3 days, and get hot/chills at night.

however, i have no pain while urinating or intense urges. after voiding my bladder i do usually have the urge to go more, and "squeeze" out as much as i can once or twice. other than that, i don't wake up in the night or have sudden strong urges.

i've thought that it might be a UTI, but can you have one for three weeks without developing pain or more classic symptoms? also, i've been told to be checked for STDs, but i've never had sex so i wouldn't think they'd be applicable.

ANY HELP IS MUCH APPRECIATED