I used up all my data and cant send regular text messages ?

So I used my data for the month and my iPhone SE does not let me send picture messages to any phone that’s not an iPhone. I can send iMessages thru WiFi but if I’m texting someone with an android, pictures won’t send. I can text them and call like regular but I can’t send picture messages to them. I also can’t reply to any group chats? And sometimes I get the messages from the group chat really late. Me and my boyfriend have the same phone and we’re in the same group chat and I’ll see he has all these messages in the group chat that I didn’t get. This has never happened before. Even when I ran out of data before I was still able to text group Chats and send picture messages to ppl with androids. This is a new problem. Does anyone know what it could Be?