Also note that the level 20 you get a serious increase in deflection (main defensive method, since mitigation is low), as well as a very noticeable increase in damage. My fists went from doing something like 20-ish average damage to around 40-ish average damage. Not sure about weapons, but I think it increases for everyone at 20th.
If some of the creatures are spilling over into "20th level+ can kill them for xp", then the encounters may seem kind of skewed for the next level or two.
Once you reach 20th, your subclass abilities (Ignore Pain is very nice for soloing for example), and quest based rewards (weapon from subclass, armor quests start), things will start to gel.
The beginning levels, prior to being 20th level, are all still "apprenticeship" levels. You are not really fully into your focused path yet, so your abilities are little more on the generic side. Once you've specialized, gain the power increase from 20th, and have access to greater equipment, you'll have a better time.