If I had an abortion and have diarrhea does that mean I have an infection?

No. Doubtful if your diarrhea means that you have an infection after pregnancy termination. An infection is more consistent with pain and fever.
Infection. Signs of post abortion infection can include foul smelling vaginal discharge, fevers, chills, pelvic tenderness or bleeding associated with severe abdominal pain. Loose stools without other symptoms is less likely to be an infection related to an abortion.