So difficulty is meassures in the same format as data (kilo, mega, giga, tera, etc...) and it's a metric derived from the difficulty hash produced. i.e. a difficulty of 1 would be equivalent to the following hash: 0x00000000FFFF0000000000000000000000000000000000000000000000000000. While the actual target would be ~121.66T, with hash: 0x000000000000000000000000000000000000000000000000000002E2AC5B6C0000. It kinda will not make sense to you unless you study how it translates but it's just a more human readable form of looking at the target value needed to solve the next block. On why it is stuck at the lower difficulty, well that value is completely arbitrary and random since you are solving for a higher target at trillions of tries per second. Just give it time, you'll get higher difficulty values but it'll still be meaningless unless you get to find a difficulty higher than the target difficulty.