It is tough to figure that out... For me, I like to compare being alone with being with someone, in order to determine what their energy feels like or how it effects me. Most of the time it feels the best (physically and emotionally) for me to be alone, but there are certain times when I'm built up by the energies of others. e.g. laughing with someone
A good positive affirmation for you: "I am strong, inside and out."
The times when I tell myself I'm weak or "can't protect myself" are the times when I feel most vulnerable to other people and the world.
1.) Look at the Free Empath Training if you haven't already.
2.) Personally, I find that spending time by myself allows me to learn to distinguish my feelings; if being alone for a little while doesn't work; go into nature, meditate, chill for a while all alone. Sometimes, it takes a while to let go of other people's emotions. I also tend to be a bit overly analytical and try to trace my emotions back to the trigger of those emotions. E.g. I feel angry. Has anything happened recently that would account for this emotion? No? Okay, let me leave this space when I have the chance. Do I still feel angry? No. Okay. That wasn't mine. I will try to let that emotion go.
3.) I agree with kit kat. Some people tend to have an angry energy; some people have a happy energy. Comparing how you feel around others vs alone helps you distinguish where some of those feeling come from and can help you decide which people may be more healthy for you to be around.