Crush's Birthday

Hi everyone! My name is Kayle and there's this really cute guy I like named *David*. We're both turning fourteen in around 3 weeks (his bday is the 31st, mine is the 3rd). We met at a summer camp (day camp) and when the camp ended we got each others phone numbers and started texting each other daily. He goes to a different school than I do, so we haven't seen each other since the end of July. While we were texting, he started texting me really sweet compliments, but in the beginning of September he stopped texting as often as he usually did. Nowadays, whenever I try to text him, he'll answer in a couple of days, or totally ignore me. I know I shouldnt, but I still really like him. Since his birthday is on the 31st, I was planning on texting him something sorta flirty, but idk what to say. Any advice?