13 week puppy had a few spots of blood after urinating....
Hi
Blood in the urine usually means that there's some irritation of inflammation somewhere.
The most likely cause is a urinary tract infection. This is actually fairly common in puppies and seen more often in females than males.
Other symptoms of a UTI usually include frequent urination with an urgent need to 'go', although sometimes the pup will only pass a few drops of urine.
It's usually easily treated with antibiotics, but if left untreated it can affect the kidneys and become a more serious problem.
I'd recommend that you have your pup checked out by your veterinarian and let him/her know what's going on. That way you can get an accurate diagnosis and the treatment she needs.
Hope this helps, best of luck.