If you didn't notice it before now, it likely isn't the world-ending catastrophe you are thinking. I was born with pectus excavatum, one of those sunken chests you saw, and just last year I underwent a surgery to correct it. The surgery was mostly a success, however I must spend three years with two steel bars inside my chest, and the surgery was, how should I say, a horrific experience. Also, very, very expensive. My ribcage is also deformed in a separate manner so there is still a little dip. I intend to cover that up with muscle as I get back into my strength training.
However, my excavatum was pressing dangerously only my lungs and my heart, and even though no serious consequences had arisen at the time, it was only getting worse. I had noticed this deformity all my life, and led to be being self-conscious to the point of avoiding any social situation where my shirt would be off... swimming, sex... even just changing clothes became the ultimate embarrassment.
You are certainly not alone. I became deeply depressed by my condition which led to my opting for the surgery (but even then I would only do so if it would be a health risk in the future: Indeed, they will not allow the surgery for purely cosmetic reasons. But try to keep your chin up... it doesn't really seem that bad to me, but then again I am going on nothing but an alias and a limited description. What you have, though, is pectus carinatum, or the opposite of my excavatum. Again, if you did not notice it before now, you will likely get over it: Imagine being haunted all your young life by it, you are twenty-one I imagine? It cannot be that extreme.
This is where I am going to be a little rough: Fuck the plastic surgeries... start eating reasonably and exercising. Start a complete chest building program, hit the weights heavy and you can fill that 'excess' area with muscle. A little carinatum can be a blessing in disguise: If you can get your pectorals to match, or just almost match your protrusion, you can have a pretty incredible chest. Again, I am going on assumptions, but a good fitness program would be good for you. Melt that fat off naturally, tone yourself up, and become sexy all over. When you are sexy all over, your faults, even serious, become little more than endearments and talking points if you can back it up. A weasel of a guy with carinatum is going to look like a foot, a fit guy with carinatum could end up Superman. Even if with my full-on excavatum, and I assure you it was not minor, I found the power to be sexy. I have incredible legs, and one of the finest asses I have ever seen. My chest? Yeah, it sucked.
Sounds like you might also be dealing with a loser "professional" as well. "Pigeon chest" is not a medical term, and you should never tell a patient coming in for a corrective surgery that something else is explicitly wrong with them... in bad form to be sure. Plastic surgeons, and you yourself, it seems, are concerned with an ideal of perfection. Give it a rest! Focus on your good aspects, while you bring your bad ones up to speed. I have puffy nipples... I used to hate my puffy nipples! But now they are kind of sexy. Actually, I know they are sexy. All the teasing doesn't seem to add up when you've got people loving on your tits. Just remember that beauty is incredibly relative: The Ancient Greeks thought a large penis was an embarrassment. That, sir, did not hold to the test of time.
You are fine. Unless it is extreme, then you are not, but if it was enough for you to not notice at all until someone else essentially teased you, then not bad enough for you to just go "whatever," and have to look it up... you are okay. The surgeries are also not fun, they are more like tortures. If I had to describe the first two or three months of my experience, it would be like having two javelin shoved through your body and left, yes left, for months. All you can do is lay on your back: Of course, the drugs given you for the agonizing pain keep you asleep for weeks on end. Then you have the side effect of almost dying because you become critically constipated and throw up all over. Ever throw up with steel bars in your chest? I am a professional martial artist and was a competitive Jiu-jitsu player, I have had my body tested to it's mortal limits, and nothing compares. Was it worth it? Yes. Would I do it again? No.
You are young, you have a lot to live for. You actually do, it doesn't seem that way, but you do. Get out there and start making yourself great. I am severely depressed, but I channel my depression into fuel. I hope you can find peace in your mind to accept yourself.