What Causes Eyes To Be Sensitive And Red In Colour?

I wear contacts Ive had them for years. I have the kind you can sleep in. I woke up this morning with my eye light red and very sensitive to light. I took it out washed it and out in eye drops. It took away the redness and i popped my contact back in but it still hurts a bit when i look at the computer screen like bright lights. Its only on my left eye though , what do i do. Did i put in my contact to early. Should i wait a hole day. Are there eye drops to take away eye pain. It isnt so strong but still it bothers.