League Play: Goals not counting because of whistle

This just happened to me rn because I literally checked in replay and there was no offside at all and I was on a counter attack and I was in a one on one and scored but it wasnt counted because the ref blew the whistle but first of all why even is the whistle blown?? Im lit in a Bundesliga title race and it's tight and that one goal would've made us go 2nd but the script said Nuh uh