Thanks for writing in to Healthcare Magic!
Human body is the most complicated system on earth and the doctor is the person who knows some of it, so it is never a waste of time to go to a doctor to get evaluated rather it can save your time that you might spend in misery or sometimes get no chance to waste it at all.
UTI hardly ever causes absent periods rather you might be having a hormonal
Three HPT in a row give a good sensitivity and indicate probably you are not really pregnant
I would advise you top have an ultrasound
abdomen to rule out pregnancy
and to detect if there any structural problem apart from pregnancy causing all this.
If you have any further query please let me know I would try to answer it for you.
Wish you a great health!