Presence of visible blood clots in urine is called gross hematuria or macroscopic hematuria. This signifies any underlying medical conditions which needs investigations to confirm. Most often it is related to urinary tract problems like kidney stones, inflammation of urinary tract, prostate enlargement, renal vein thrombosis, certain kidney tumors and polycystic kidney disease, blood coagulation disorders and anticoagulants.
I suggest you to consult a urologist soon as you are having a history of kidney stones as well.
I hope it helps. Take care and regards