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The burning and pain during urination could suggest a UTI. The spotting could be due to the hormonal imbalance after taking high dose emergency contraceptive. If you have taken Plan-B within 72 hours of the intercourse, then chances of pregnancy are not there. If there was delay in taking emergency contraception or if you had intercourse again after taking it, then chances of pregnancy cannot be ruled out.
Visit your gynecologist/healthcare provider and discuss your symptoms, get examination and tests done to confirm the cause for your symptoms, and get started on appropriate treatment.
Take care.