It's a 4 digit code. If it's used every day even once, how do you forget it? If it's brand new and you only used it once, I might buy that. But that doesn't appear to be the case. Can you explain how you got to this point? To be honest, it sounds like it's not your phone. People don't normally forget a 4 digit passcode. That said, you have 10,000 possible codes to try. But, depending on how it may be set, it could wipe the phone after 10 unsuccessful tries.
Sent from my ancient but trustworthy iPhone 5