a.
1.
Tormenting, torturing, agonizing, racking, distressing, distressful, excruciating.
2.
Grievous, afflicting, afflictive, distressing, disquieting, troublesome, displeasing, provoking, annoying, vexatious, unpleasant, disagreeable.
3.
Toilsome, arduous, difficult, hard, severe.