I have a three month old son, he is my first child. So I know this from recent experience.
Before I knew I was pregnant I had my period but then I had bled for a very long time. I found out I was 8 weeks pregnant. Because I went to the doctor thinking I had a stomach bug.
Symptoms of early pregnancy include:
Nausea and vomiting
Breast tenderness
Food cravings
Spotting: Which is bleeding very little, the blood shows up on toilet paper only and the color of it is very light sometimes it may look orange or pink.
Heightened smells
Back pain
Fatigue
If you're experiencing any of these symptoms I would take a pregnancy test.