My phone's touchscreen isn't working from time to time

My phone's touchscreen isnt working properly every now and then for around 3 seconds and then becomes normal. Why is it happening? It is like someone keeps touching my touchscreen and not letting me press buttons correctly.(makes games with D-Pad control unplayable).I can recognize it whenever i need to hold a button or swipe something. Even if it is probably my phone I just want to know why this happens in the first place? Why does it happen only every 2 hours or so? Why doesnt it just happen anytime? Help?