Jess...when you get "overloaded", when do you notice? Try observing yourself so you know when you start picking up negative "vibes", and not when you're already being overwhelmed.
Then, when you feel this happening, think of something that makes you happy. A happy tune, some movie that had you laughing, a puppy, a kitten, whatever gets you all smiling. Add in perhaps the feeling of sunshine on your face, and you should manage to shift your focus from somebody else's emotions to something happier.
Also, just locking everything else out for a few seconds and focusing on your breath might help. Imagine you're taking in the smell of hay, fresh flowers, a freshly mowed lawn, anything that for you is connected with pleasant memories.
Let me know if this works for you.