I get that you have social anxiety and that can be debilitating in this circumstance but please try and do your best to get help this time. Maybe ask a parent or friend to make the appointment for you if phoning makes you anxious. This could be serious if left untreated, so please go and see your GP.
A UTI cant be treated by just drinking water and generally needs antibiotics, if that's what your problem is. You need to see your GP.