Vaginal discharge

I have been having discharge with a slight color of blood. I had back pain and lower pain near left side of my stomach and sometime some pain in the vagina. So I thought it could be a uti. I went to my doctor and with a urine test they said I was negative to uti but that since I had blood in my urine I had to take the same antibiotics they were giving me for uti. This antibiotics at least one the sulfamethoxazole makes me feel horrible. So what I want to know is has anyone experience this ? And what were your steps to curing it ? Or what advice can u give ?