Online dating is a great way to “meet” lots of men and filter quickly through those who may or may not be right for you. However, appearance is important in a relationship, so make sure you don’t use the internet as a way to keep from presenting yourself in person to a man. Post honest photographs of yourself in your profile, and that way, you’ll know that the men who respond to you online are responding to all of you, and not just part of you.
I know you’re self conscious about your weight, but unless you decide to lose some of that weight, the best way to gain self esteem is to understand that the men who do respond to you online, are responding to you AND your weight, and that they find you attractive as you are.
As far as questions about your being single, you should be honest and say you’ve never really had a relationship and that you’re a late bloomer. There is NOTHING wrong with that answer. You’re 21 and not 41, and it’s understandable that people who are 21 may not have had a lot of dating experience yet. In fact, some, just like you, have never really dated at all.
Honesty is the best way to intimacy and intimacy is a building block of relationships, so practice telling the truth without baring your entire soul online, and see how that works for you.