In my personal opinion (yes i bring a personal opinion to the Internet, yes nobody give a f* and yes i hate u all but my mum love me and say i'm beautiful wich is nice), lowers levels are
always the same special awesome kind of magic feeling for the new toons.
You just discover and rediscover the world, the lovely peace of starters zones (aaah WestMarch, Teldrassil, The Barrens... atmosphere and soundtrack) where nothing actually matters but fun, thousands of newbs running half naked with ridiculous butter knifes through the world ... This occurs for the [ 1 - 20 ] levels.
Then levelling go darker and darker as you power up ; everybody just think of his personal stats and profits, mounts make you more alone, quest taken in STV make you kill 400x Devils Ants in a overcrowded unfair-pvp genocide zone and give back in Winthersprings, while you actually play 12h for 1 level.
The solution is ; DON'T CARING on being 60 as fast as possible !
Up your main professions. Fish a bit ; it changes and actually bring money if u know how to do it. Make battlegrounds. Socialize !
Apply this and your levelling, even if 2x longer, will paradoxically feel 2x shorter (than off-brain overgrinding for example) !
Cheer up, adventurer