Hey there….having a 3 day fluctuation in your cycle is not too uncommon…Typically tender breasts is also a pregnancy symptom, not just associated with your period…It could be that your uncomfortable feeling in your tummy could be that you are going to start your period soon, it could also be something else….Anytime you engage in sexual activity you can risk pregnancy and or sexually transmitted diseases….I would suggest taking a pregnancy test, first thing in the morning is when they are most accurate, also you could be seen by a doctor to rule out any possible infections…I hope you figure it all out soon and that you will come back and let us all know that you are ok! Love Meg