Gas cap issues!

Alright.. so in the last couple weeks this has been occuring. So if I stand behind my car at idle, you will her "Pshhhhh" literally sounds like air is just leaking out of a small hole of something of that such, right around the gas cap area.. almost exhaust/underneath area.

So.. I didn't think much of it.. was like, we'll its not affecting anything. Actually thought I possibly had a minor hole in my exhaust a couple weeks ago but that definitely isn't it. Ok so when I go to fill up my gas tank, especially if I haven't for a while and I tank the cap off "Psshhhhhhhhhhhshhhhhhh" and you can literally see the gas vapors coming out, it stinks to. Now first time this happened I waited 3-5 minutes till it stopps, filled it up.. worked fine, full tank. Went on driving, still hissed at idle.

Now next time I went to fill it up, took off the cap.. same thing "pshhh" so I just try to fill it up.. This is where I realize it is a real problem, try to put gas in and put about 3 dollars on the ground, 1 gallon of gas all shoots back out. So I am curious to whats causing this.

I was thinking its possibly.. my gas cap? has a crack in it? isn't working properly? anybody! help is very appreciated.