yes kidney or urinary tract infection or maybe nothing however get checked immediately.
Blood in semen is called hematospermia. It can occur due to many conditions such as infections, swellings (inflammations), cysts, stones & other obstructive lesions, and benign or non-benign tumors of the organs of the genitourinary system (involving the bladder, urethra, the testicles, the seminal vesicles, the epididymis, the prostate gland etc).
Investigations include blood tests, routine & culture tests of urine & semen, ultrasound & MRI scans of genitourinary system, and histopathological tests (FNAC, biopsy etc). So, I suggest you to consult a General Surgeon for a thorough medical check-up and appropriate tests as you might need treatment (medicines and/or surgical intervention) for management of your condition.
I hope it helps. Take care and regards.