Yellow crusty patches of skin on scalp?

I just came back from a day at Soak City celebrating my friend's birthday on Saturday. Yesterday I touched my head for whatever reason and it was wet on top. Thinking it might be blood, I looked at my fingers but it was just clear liquid. I had taken a shower the night before so it couldn't be water. I didn't think much about it so I just continued with what I was doing.

Around 4 hours later I touched my head again and I felt a small patch of dry crusty SOMETHING on my head where it was wet. I picked at it and took it out (gross, I knoow) and it was yellow crusty stuff. It wasn't all over my head just an area on my scalp near the back but still on top. As usual with picking scabs and that kind of thing I kept picking at it because I didn't want it on my head. After I picked it all away a few minutes later my head started throbbing and I got a headache. I took two Tylenol pills and went to sleep.

This morning it was better and I felt my scalp again and it was there again. I picked it again which probably wasn't smart. It doesn't throb but when I touch it it feels sore. My mom says that it might be from the chlorine in the water from Soak City. What is this and what should I do about it?? Is it serious? Thanks for your help.