I have had traces of blood in my urine, but blood tests are ok?

Hi i have had traces of blood in my urine when doctors do the dip test they say every time there is blood.but when they send it of it comes back as normal and i am in so much pain with left side of my back going into my tummy i cant even stand can this be connected as really worried and have 3 kids to look after

Age: 30
Female
Medications: Neflex and codine