Can drinking too much coffee be harmful, and if so what kind of side effects does it have?

I DRINK AT LEAST 30+ OUNCES OF COFFEE DAILY , I HAVE BEEN DOING THIS FOR OVER A YEAR . I ALWAYS DRANK COFFEE BUT NOT TO THIS EXTENT. ICANT NOT HAVE IT I GET SICK OR IS IT IN MY MIND? AS OF LATELY MY STOMACHE HAS BEEN WREAKING HAVOC CAN THIS BE FROM THE COFFEE?