Just curious ...ladies Help?!

So when ever I’m humping my pillow ( the only way that I feel any pleasure) I keep going but then I get to a point where I have to stop right when it starts to feel good ! I don’t know if it’s because I’ve already orgasmed ? I don’t know if it means I’m on the verge of it ? I don’t know if it’s because I get too tired it does feel good when I’m done but it’s not like any fluid ect comes out sometimes just a white discharge on panties

Just curious to see if anyone else can relate I’m also a virgin I’d love to hear what you think about the situation