My Iphone 6 has already used to much cellular DATA

My Apple Iphone 6 is on ATandT. Its 16 GB. My family shares 15 gigs per month. 5 of us share the data. It had just restarted 2 days ago, and my phone has already used 6 gigs! My Wi-Fi hasn't been working, and when i go onto youtube or something, i come back out and my Wi-Fi is off. I have reset my Phone, I have updated my phone, i have done everything possible. The only thing i use with DATA is my Spotify and some instagram. I know spotify takes up a little DATA, but this is just ridiculous.

Only you can find out how you are using data, no one here knows.