As tcomea2 has pointed out, you definitely have an Approach Anxiety. As I have read, it comes from your recent shift of "not-being-so-social" to the "recently going out at night" routine. Don't worry about it, everybody has approach anxiety - even I had that when I was starting out to dating women.
You only have to be comfortable approaching people, groups of people or women in particular.
To do this, try this SIMPLE approaching exercise in a week or so: In any time of the day, whether you are strolling or going somewhere, try to approach a person you don't know and ask for directions, what time is it; where's the nearest place to go for something this or that, etc. Do it every time an opportunity comes.
With that exercise, you are training yourself (and your body) to be comfortable when approaching a person who you don't know completely. It also allows you to be social and improve your communication skills. Remember that simple conversations with people you don't know can greatly affect how you interact with strangers you may meet in the future.
When approaching someone, NEVER assume that you are going to be rejected something BAD is going to happen - remember that these things are all just there in your HEAD.
Instead of negative things playing in your head, think of the POSITIVE outcome that you can get out of approaching a person or a group. Think of gaining new friends or feeling happier because you have someone or some group to socialize with. Think of gaining an opportunity to interact with people and improving your SOCIAL skills.
If you get rejected or feel awkward - that's a nice thing, in a way that you must definitely EXPERIENCE a lot of negative things before you get used to it and somehow DEAL with it in succeeding opportunities when meeting people.
Remember that having experiences of rejection enables you to formulate SOLUTIONS of your own, if in case a typical scenario you experienced in a past is similar to the one you are experiencing at that moment.
Having a feeling of getting rejected? TAKE THE RISK. You will never know what will happen so why worry even though you don't know the outcome? So instead of standing there and waiting for something, INITIATE and see where your actions (positive ones) will take you.
So far, I can first offer those pieces of advice on approaching. If you want to learn more what to do after a SUCCESSFUL approach, then feel free to ask and reply.
We are here to help you.