What about other passwords you were using at the time? Can you remember any of them and have you tried them?
Do you have any idea what the password might be, based on the way you generate passwords? If it is completely random characters then your chances of brute forcing it are very small. Or is it more likely that you chose a dictionary word or some other word which has meaning for you?
You say you think it will be short and not have any special characters - that's a start. What about numbers? What about uppercase/lowercase?

If you can't remember the decryption password, then you only option will be to attempt to brute force it, but as pooya87 says above, unless you can be more specific about what format the password might take then you are likely wasting your time.

With which character does your private key starts? 6, 5, K or L?
Because the "passphrase" might be for Brainwallet, not for BIP38 private key and you might have a bare WIF prvKey all along.

If it's any of the above but "6", it not encrypted.

How long a passphrase are we talking here? You need a length range to brute-force effectively: something like between 8-12 characters or of the sort.

You lost the whole encrypted password. You will not be able to recover the coins. The coins are gone. Sorry. If few characters were lost, btcrecover would have been helpful.

You can always try to brute force it as mentioned above, or by using a service like WalletRecoveryServices, but unless you have a clear idea about the complexity (length, if special characters were used, etc.) of the password, these services are not going to be of too much help.