Need advice!!!

Okay so I'm three days late but my period are messed up so I'm not going to test until the 20th , but now every time I stand up my lower back is killing me and my lower belly to and not like cramping just hurt in and when I pee my lower belly hurts for like 30 seconds then goes away , but I get kidneys infections a lot because I can't seem to make myself drink enough water. just wornding if this is a sign of pregnancy or something else and if it is something else what do you think it is????