October Novel Prep Challenge

I'm struggling to know who my antagonist is.

My story is fantasy western about a cowboy who agrees to give a message to someone, not realizing she's not in the current town and he'll have to travel for several months to get the message to her. Since the message doesn't even mean anything to him, she's not always sure it's even worth the trouble.

Possible Antagonists
1. Himself--he has to grow, of course, and part of that growth includes doing what is right, even when it's hard and he doesn't want to. As in any good story, my MC struggles and eventually wants to quit.
2. His Father--My MC's father left him and his mom when MC was a kid and it caused his mother's premature death. He later leaves his own wife, not realizing she's pregnant, and when he decides he should return, she's since died in childbirth, along with the baby. People say if he'd been there, he could have gotten the doctor and they both would have lived. Later, he meets his father again and at first he is angry and resentful, but later saves his father's life and the reconcile. In the end, the message is being delivered to a pregnant woman and he decides to stay with her to help her, having recovered from his daddy issues.
3. Nature--Lots of things try to kill my MC throughout the story as he almost drowns, almost suffocates in sand, is almost driven mad by a lack of sleep because the song crows won't shut up, etc.
4. Various "Bad Guys"--My MC meets various bad guys along the way with 1 set, the spur hunters, being a recurring theme, at least 3 times, but I hadn't planned on them being the same set of spur hunters since the MC is traveling so far. It's more like they are sort of gangs and he's traveling through their territories where they hunt for humans to get their spurs which are sometimes made of a precious metal with mystical properties that allows them to communicate with their mounts, but also, they just enjoy the sport, like deer hunters, and they display their spur trophies proudly.
5. Life--He feels like life is pointless and meaningless. He has no purpose and doesn't see that other people often do have purpose and meaning in their life. He finds this through his effort to deliver the message.

I don't care that I don't know who my antagonist is, but apparently, I'm supposed to know for some of the exercises.