What Causes Blood Discharge While Urination In A Kid?

My 2 1/2 yr. old Havanese has had blood in her urine two times this evening. She urinated after I found the blood and it was fine. She had been licking in that area since being groomed 2 days ago. She is eating, drinking and playing as normal. What can I do tonight for her ? I am worried until I can get her to the vet tomorrow if they are open. We have terrible weather conditions of about 15 inches of snow with rain, sleet and another 3-6 inches of snow in the morning. Please help. I have antibiotics but I am afraid to give to her without knowing how much and if what I have is ok to give her. Amoxicillin