When do you first get symptoms of pregnancy?

About 3-4 weeks.. I felt tired and started to have loose stools and tummy ache. I even went for a 11km marathon when i was about four weeks pregnant! Was feeling exhausted very early Into the run and thinking how bad my stamina had become. Little did I know that I was pregnant. About four weeks into it I missed my otherwise regular menses and I suspected I was pregnant. About the same time I keep going to the loo and having weird tummy ache. And I really did notice my breasts and nipple starting changing, they seem swollen and more engorged