You have a UTI and found Strptococcus B in urine culture. Either hypothyroidism
or "O" positive blood is not the cause for a UTI. Tab Synthroid
you can continue as per your requirement.
What you need is a urine Culture & Sensitivity - that will clearly indicate what antibiotic is sensitive and to be taken.
What you need are - Plenty of water, Barley rice water, urine alkaliser, mild diuretics, appropriate antibiotic.
If you repeatedly get symptoms do a USG abdomen for KUB evaluation