4 months. 4 MONTHS. Don't worry! It's been only 120 days. We progress differently as Chris says, some might get it in 4 months, others in 1 year or so. Believe me slow result is better than no result, I'm sure you have gotten closer to the muscle up but just don't realize it.
Now as for tips, I'm guessing you know the technique, see if you're missing something:
-Swing forward, and when swinging backward do a knee raise and pull up together, but pull backwards and up, not only up.
-Once you reach about chest-to-bar level, start pushing down on the bar like you imagine doing tigerbend push ups or even shuttle push ups (this one is crucial hence the transition part is the hardest) and start extending your legs (from tuck to extended).
-Lean forward with chest till your chest & elbows are over the bar and finish with a strong dip.
Now a lot of people have strength and don't have the technique and vice versa, they have the technique they just don't have strength, so it might be a little of both strength and technique, or if you have fat (extra weight) it is a lot harder to do it (but it's not impossible nor an excuse).
Keep training, make sure you master the basics-form&everything (might take even half a year to do so, so don't worry), and I'm sure you can get it if you want it bad enough. Investing in a resistance band is also a good way to learn it.