A couple months ago I went to the dentist so that they could put a cap on top of a tooth that lost it's feeling and was barely there. Well now my gums have a red lining around the cap, it smells horrible, and I guess it's pus that's coming out from underneath it. The cap isn't loose or anything. I've used mouth wash and I scrubbed it more than usual but nothings helped. I heard that you can die from this but I don't know. So what's happening to me? How can I stop this?

Your not going to die from that, maybe there is some excess crown cement under the gum line? Try to floss and brush it out for now, but you HAVE to go back to the dentist to get it sorted out, ASAP

Definitely go back to your dentist. You want to rule out an abscess.

Make sure when you floss around the crown that you are going UNDER the gum. Wrap your floss in a tight "C" shape around the tooth and gently slide it under the gum and scrape the side of the tooth with the floss as you come out. Use an up and down motion with the floss, not a back and forth motion. You may find the floss catches on something under the gum. It could be excess cement as Amir said or it could be that the crown is ill-fitting.

You can also dip your toothbrush in some baking soda and GENTLY massage the gum. Rinsing with some tea tree oil mixed with water could help also. (5 drops of tea tree oil in 1 cup of water. Mix it well and use the solution 2 times daily making sure it reaches where the crown is.) Crest's ProHealth might help as well.

Good luck.