Without you really explaining what qualities you hate all we can do is take a guess. You might want to elaborate on what tone you're getting now that you didn't get before. Without that information it sounds like you just don't like the "new sing sound" so i'll address your question from that angle.
New strings will have a zing & bright sound to to them. Is this what you're hearing that you hate? Worn in strings should have a darker, warmer tone.
Over time strings will stretch out. That stretching combined with the oils from your hand will mellow out your strings giving you the type of tone you liked w/ your 4 month old strings. Problem is, at some point you're going to have to put on a fresh set (broken strings etc). Sounds like you might need to select a set of strings that are less bright when they're new. This may take some experimentation by trying different sets but might be worth while considering you "hate" the "new string sound".
A few things to consider are:
- don't buy stainless steel strings b/c they're super bright
- chrome and pure nickel strings are mellower
- nickel plated strings are in the middle
- coated strings (like Elixirs & Ernie Ball Coated Slinkys) sound more mellow
- a thicker gauge set (11's and up) will have a beefier, warmer tone than thin strings
- flatwound strings will be super mellow
If you're playing jazz n stuff like that I'd suggest you try flatwounds. That's probably not going to cut it if you're into heavy rock etc but, hey, you never know.
As far as putting the strings on improperly:
Its possibly but not likely. Most common symptoms of not putting strings on correctly is that they'll be hard to keep in tune or they'll just break.
Another, non-string, related thing you can try is to turn the tone knob on your guitar down. That will easily mellow out the guitar's sound & won't cost you a dime.