You already mentioned the most important point in your comment to Tim's answer: you probably hear the notes of the pentatonic scale as the most consonant notes. Those notes usually sound good over all chords from the respective scale, whereas the remaining two notes can be problematic over certain chords. E.g. in C major the two notes that can be a bit problematic are the F and the B. For this reason, these two notes are not part of the C major pentatonic scale. The F is even more problematic than the B, and for this reason it is also called the avoid note of the C major scale. If you were to play an F as a target note (i.e. a note on which you rest for a while) over a C major triad, then it would clash with the major third of the chord (the E), hence "avoid note". Of course, it can always be used in a different way, e.g. as a passing note. With the pentatonic scale you don't have that problem, you don't need to think about the rhythmical placement of the notes, because they will almost always sound OK.
Note that in the relative minor key, i.e. in A (natural) minor, removing the same notes (the F and the B) also results in the A minor pentatonic scale. Again, the note F is the avoid note because it clashes with the fifth of the A minor chord (the E).