Phone is stuck on the same app!

So my phone had been working fine but since I updated it to iOS9 I feel like it messed my phone up. I was on Instagram for a while and I tried going to my home screen with the button and it wouldn't. I tried going to my hoe screen with the home screen option that the little ball option has on the screen and it wouldnt. I locked my phone and when i would try to unlock it, it wouldn't. I would give me a black screen. I thought it was dead so I plugged it into the charger but it only made the noise that it was charging but still the black screen? I places my finger on the home button and it unlocked? I need help! :((((