A ‣ Nouns relating to difficulties 
Fairly small difficulties: a snag, a hitch, a glitch. Glitch usually refers to a technical problem of some kind; the other two words are more general.
More important difficulties:
A setback means that progress has been stopped by something.
A stumbling block is something that prevents action or agreement.
A pitfall is an unexpected difficulty (often used in the plural).
An obstacle is anything that stops progress, either literally or metaphorically.
An impediment is something that prevents free action, progress or movement.
A dilemma is a situation where a difficult choice has to be made between two, sometimes unpleasant, alternatives.
An ordeal is a severe experience, which is very difficult, painful or tiring.
B ‣ Adjectives relating to difficulty 
adjective | meaning | collocations |
problematic | full of problems or difficulties | relationship, situation, concept |
abstruse | difficult to understand | theory, argument, philosopher |
arduous | difficult, tiring, needing much effort | climb, task, journey |
complex | difficult to understand as it has many parts | issue, problem, theory, process |
convoluted | unreasonably long and hard to follow | explanation, sentences, theory |
gruelling | extremely tiring and difficult | journey, work, match, expedition |
insufferable | difficult to bear, as it is annoying or uncomfortable | behaviour, heat, boredom, pain, person |
obstructive | causing deliberate difficulties | person, measure, behaviour |
tough | difficult to deal with or do | time, job, climate, decision |
traumatic | shocking and upsetting | experience, past, childhood |
wayward | changeable, selfish and/or hard to control | behaviour, child, person |
Common mistakes
Difficulty is used in the singular in the expression to have difficulty in doing something: I had great difficulty in finding a job at first (NOT great difficulties).
C ‣ Informal expressions relating to difficulties 
Oh dear, more homework! What a pain! / What a drag! [What a nuisance!]
The software is good for editing still images, but editing video is a real chore. [boring job that has to be done]
What’s eating him? / What’s got into him? / What’s bugging him? / What’s (up) with him? [What’s the matter with him?]
I can’t face the hassle of moving house again. [situation causing trouble or difficulty]
My daughter keeps hassling me for a new bike. [asking again and again]
Having to listen to him singing is sheer torture! [used figuratively to refer to an unpleasant experience]
to slog (your guts out) / to grind / to graft / to flog yourself to death [to work hard]
in a fix / in a spot / in a hole / up against it / up to your neck [in a difficult situation]
The company’s in a sticky/tricky situation now the workers are going to strike. [difficult]
I think I’m off the hook / in the clear / out of the wood(s) now. [freed from a difficult situation]
The downside of living here is the traffic thundering by. [the disadvantage of a situation]