It is not uncommon for trainees to spend weeks or month pounding away in the gym, just to realize that they actually look exactly the same (or even worse) then they did before.
Why does this happen, and how can you prevent it?

First things first
Assuming that your program is well designed (you are using the right exercises and performing them correctly with intensity), the answer is usually a simple binary function: you are either undertraining or overtraining.
While overtraining is rare for the average, barely-motivated, part-time gym goer, it can actually become an issue for athletes like yourself who are pushing themselves to the limit on a weekly basis.

The fact is, your body grows outside of the gym, when a cocktail of hormones is released to stimulate recovery as a result of muscle damage occurring from a productive workout. Unless you are on muscle-building drugs, which can vastly increase your work tolerance, your body does have a limit in regards to how much lifting is actually beneficial. It does you no good to keep tearing down muscle fibers if your body is not able to synthesize enough hormones to keep up with all of the damage.

Lifestyle does matter

Another thing to consider is that a stressful lifestyle, including long hours and insufficient sleep, will negatively impact your hormone levels, and therefore your recovery ability. There is a reason for the term “professional athlete”; these individuals literally have no job other than to train, recover, and compete. They sleep and eat perfectly. They do not drink alcohol or smoke.
These individuals are able to handle a much higher training load then someone working 60+ hours per week on their own business while also being responsible for two small children.

I say this not to scare you away from hard training; it is just important to understand that there is more to making progress than “blasting your delts” and “going beast mode” in the gym ( Yes, Facebook can be wrong!). We need to track objective measures of progress to make sure that we are not just going in circles.

How to measure progress?
The simplest way to know that you are gaining is to pay attention to your strength levels on certain compound exercises. Past the novice level, when you can make rapid strength gains due to increased nervous system output, there is a strong correlation between muscle size and strength.

While this does not mean you should train exclusively like a powerlifter, you do need to know how much you can weight you can move on a key pressing exercise, a pullup or row variation, and squatting exercise.
For example, if you are stuck squatting 225 lbs for 10 reps for a month, do you really believe that your legs are growing?

What to do if you are overtrained?

If this happens to you, it is time to reevaluate your training and see where you are overworking or under-recovering. Taking a deload week once every month is a tried-and-true strategy. It does not have to be any more complicated then cutting the total number of working sets in half for one week.

For example, if your normal chest routine is 8 sets twice per week, keep the same schedule but reduce it to 4 sets. Remember, if you are still lifting the same size weights as when you started, you are not any bigger!