Embedded UTI?

I'm 22 years old and started with symptoms when I was 17. It started with frequency and then a few days later I developed an uncomfortable feeling of pressure over my bladder. I went to walk in centre and there were white blood cells in my urine and they prescribed me a 3 day course of antibiotics. I didn't feel any better after that so went to my GP and they gave me a 5 day course and sent urine off for culture (came back negative for anything.) Over the years, I've been getting flare ups every so often of either random frequency/urgency or the pelvic discomfort feeling with frequency. My urine has been tested many times but has only ever shown white blood cells. I'm currently seeing a urologist who thinks it's interstitial cystitis but when I came across info on embedded UTIs I thought it could be a possibility. I never had any bladder issues before my first 'UTI' at 17. I'm not sure if this could have caused it but I was on the last few days on my period and I didn't change my sanitary towel for 2 days I think (disgusting I know! Don't ask 😕) shortly after that the symptoms started. Could it be possible that all my issues are actually stemming from an embedded UTI? Any advice would be greatly appreciated.