Welcome to the forum!
Since you expect your periods in about 2 weeks, it could be spotting due to ovulation, which mixed with urine.This is normal.
Gross hematuria (blood in urine) visible to naked eye is also seen in kidney and bladder stones, cancer of kidney, sickle cell anemia, bladder endometriosis, low platelet count, bladder injury and bladder infections. UTI too is a frequent cause but generally causes microscopic hematuria.
The other possibility is a cervical polyp bleeding due to exercise and the blood mixing with urine.
It is difficult to comment beyond this at this stage. Do discuss this with your doctor. Please let me know if there is any thing else and do keep me posted. Take care!