Leg Pain In Child, Bruises In Purple On Knees. On Zythromax. What Now?

My 3 year old child complains of leg pain roughly 2 or 3 times a week, including last night. She woke up this morning with purplish brown bruises on her knees. It is visible on both knees but one is significantly darker and larger than the other. She says that they don t hurt, but she winces if I apply pressure. I plan to call her pediatrician in the morning but wonder if this needs quicker attention. (wait for appts can be lengthy sometimes) She had an upper res infection last week and just finished an antibiotic (zythromax) and cough med. She also regularly takes a multivitimen, fiber , probiotic , and vitimen c