Please i need someones help!!!

Every time i open app on my iphone it closes itself for 10-20 seconds after i open it. It drives me crazy! I tried to turn off and then on my iphone by pressing on/off button and home screen button, i tried to download new app and then open it and i delete all opened apps that was running, BUT NOTHING HELPED! SO PLEASE IF SOMEONE KNOWS THE ANSWER ON THIS QUESTION I WILL BE VERY THANKFULL!!! thank you