I’m 17 (understand I’m too young and wasn’t prepared for this) I ran a cycle of Super DMZ 2.0 with nothing else. I ran my PCT after. Just started a cycle of RPN Havoc and since I had such great luck with the first run of a PH I decided to not run anything with this one. I purchased a DIM and a Cycle Support incase something like this would happen. I have a pain in my left pectoral and kind of my left sternum. It started after bench press when I was working chest with barbells.
Someone else may chime in with a different answer but if it sprung up in your chest and sternum after benching it doesn’t sound like gyno, it’s my understanding that gyno will be an ache and sensitivity around the nipples and as it continues hardened masses will form. Yes you are way to young to have used any of this stuff but it sounds like maybe just a muscle pull or something of the like.