Welcome to the forums. There is a wealth of information here and, most importantly, an incredible pool of skill and experience among the users.
To answer your question I would recommend a) you stick to only one thing, especially as you are beginning and growing in your experience and b) do not approach Android development or iOS development.
Unless you are using something like RhoMobile or PhoneGap, you must learn a specific language to develop on mobile devices. Android requires Java (not to be confused with Javacript. They are quite different) and iOS requires a knowledge of Objective-C (which is highly intimidating, even to a veteran developer).
There are many avenues for you to develop responsive web pages that are suitable for mobile devices.
And, as I mentioned, when you gain a bit of confidence and experience you can try out one of those frameworks that apply HTML/CSS constructs to building native mobile applications.