If you are gaining strength you will be gaining some muscle mass – but probably not enough for your liking. Without knowing more about your workouts it is hard to say, but two very common problems for skinny guys are:

1) You think you are eating a lot, but you are actually not getting enough calories to help you build muscle.

2) You are not working out properly by lifting heavier weights with good form.

Now, if your friend has done weight training before I am hoping you are getting good form and weight training advice from him. Most likely is that you are just not eating enough if you are that skinny.

If you were eating enough and not workout out well you would put on fat. Since you are remaining skinny this means your body is not getting enough calories for fat storage, and also not enough to build muscle as well.

I cannot be certain by I would look at the amount you are consuming and try to up that across the board in 5 meals a day. It can be tough and you might think you are eating stupid amounts of food – but if your genetics give you a super fast metabolism you need to work with that ok.