I wouldn't take creatine. About 90-95% of it just goes right through your system anyways and is bad for your kidneys etc... Im thin and saw great results on it but as soon as I stopped taking it, I lost the water weight. Not worth it.
A balanced diet is more important. You get plenty of protein.
If you want to gain, eat berries, nuts and a spoon full of honey as soon as you wake up to take your body out of it's catabolic state. I grind up oatmeal and ad that to your shakes along with a scoop of peanutbutter, and wheatgerm. Oh, and barley green is the sectret to life. You should look that shit up. It's the most nutritious thing on the planet.
It taste like grass ( go figure) but you won't even notice it in your shakes.
Im not on here much so pm me if you want anymore advice.
Good luck and be careful.
oh, and water...drink half your weight in fluid onces a day. Don't drink too much it's not good for you.