Sorry to hear about your issue :(
How long have you been facing this issue?
Let's try a reset first. Press and hold the power button and the home button together until you see an apple logo.
Now check whether your issue is resolved.
Let me know.
let's reset all settings now.
Go to settings > general > reset > reset all settings
let's see if that helps.
okay let me know once it is back to home screen.
Most likely it is a hardware issue.
Double click on your home button. It will bring up all the apps that are currently open. Swipe up on the camera screen and it will go away. Now, open camera app again and see if it works
Yes I am
If that too did not work, I am afraid you would now need to try a restore.
Open itunes in the computer and connect the iphone to the computer. Your iphone would now be listed in itunes. Click on the iphone logo in itunes and you will find a restore button to the middle of the screen.
PS: There is an issue with the current software update (9.3) as it asks for your apple id and password (and also your icloud id and password) even if you enter them wrong. So I would recommend you not to try the restore for a couple of days atleast until apple comes up with another update.
If the restore too does not work, I am afraid it is a hardware issue and may need a repair/replacement. You may need to take it into any apple store nearby or call apple care to set up the repair/replacement. If your iphone is under warranty, you will get a free replacement provided there is no water/physical damage.
you are welcome. Let me know if you come across any difficulty.