Can you know if you miscarried if it's early?

My husband and I are not currently TTC because we want to be more finically set as he is in his last semester of college. However, I missed my period in March. I started to worry a bit as, again, we don't want to conceive. But it's not like we wouldn't have made it work. I was going to see if I got some other symptoms such as nausea before I took a test. Well, 2 weeks after my late period was supposed to finish, I had a really heavy period with bad cramping. I figured it was just because my period was late that it was heavy, but now I'm wondering if I misscarried since I don't normally have irregular periods. Can you know if it happens that early in pregnancy? Possibly even less than 4 weeks along? What are some other symptoms of early pregnancy miscarriage?