Help please

Daisy
I am on my period and i'm a day in, i wear tampons and there is a water like substance trickling out of my vagina but is not being stopped by the tampon, what could this be/mean? I have never had it before and i'm also having the worst period pains i have ever had, not to mention i was 5 days late on my period...? 
Please help me discover what this is 😣😊