Of its happening soon after injection, it could be the pH is screwed up or something minor of that nature. Maybe there was a small issue with that batch. Have you tried another vial to see if its the same deal? It would be easier to find out if you had done cycles before lol.
The fact that the pain is occurring later is what tells me its not just virgin muscle. Or am I mixing you 2 up. Having 2 people post in the same thread about the same issue is a bit confusing. So wait, are you experiencing pain from the get go, or from 24 hours or so later?
Because if its there from the injection (or soon after) then its most likely virgin muscle. If its coming ~24 hours later, its something else. If its so extremely painful, it could even be that the Cyp crashed and due to it having a high melting point its crystallized. But that depends on how it was made and the concentration. Perhaps they accidentally used more this batch than they normally do? Idk.