Bleeding during pregnancy may not mean you're having a miscarriage. An article by kristen Eckler, M.D., Harvard Medical School, writing for Gather:

Bleeding can be a sign of miscarriage-but it's also a sign of many other, less serious things. Bleeding in the first trimester is a very common occurrence; one out of 4 or 5 pregnant women has vaginal bleeding of some volume during the first trimester.

She goes on to list some common and benign causes of bleeding in the first half of pregnancy, including:

Some infections in the urinary tract may cause blood in the urine that stains underwear, and is confused with vaginal bleeding.