why does my Rating only increase slightly when I win ?

First of all, youre a new member, so your rating will jump around at first.
Secondly, dont get so caught up in the rating. Its just a number. As you improve, your rating will go up.

Also, the site uses Glicko and that utilizes a rating deviation (RD). A new account, or one with few recent games in a format, will have a higher RD and will get larger rating swings.
https://support.chess.com/customer/en/portal/articles/1444777-how-do-ratings-work-
It should also be noted that members are only allowed one account.
https://support.chess.com/customer/en/portal/articles/1444776-can-i-have-multiple-accounts-