(OK this turned into a mega post, but I thought it might all be helpful so kept it all in...)
I think it varies a lot for different people and different dispositions. I didn't find the actual egg collection cycles with all the injections and prodding and poking too bad. It fills you full of estrogen which tends to make me feel quite good. Also you feel like you're doing something proactive, and you're kept very busy with all the appointments etc.
Some practical info: The stims medication is fine. Ice pack for five mins before and after. If they give you fyremadel in pre-filled syringes they are quite blunt (I read someone say its like trying to inject with a spoon 😂), so go at 45 degrees with a quick, firm jab, like throwing a dart! I also had progesterone in oil injections which people describe as horrific but were also fine. Heat pack for those, and watch nurse Linda on youtube beforehand. The worst drugs for me were when I had noresthisterone before my first cycle (made me very glum) and the progesterone suppositories as they're just gross and messy (buy loads of panty liners if you're using them vaginally).
After the cycle is over can be pretty brutal - when my period arrived I was completely exhausted and hurt all over, and both cycles after EC have been bonkers (one was the shortest cycle of my life and the other the longest). And the waiting for the next transfer is tedious.
I went into things with a relatively pragmatic viewpoint, which has helped so far. Each transfer has about a 30% chance of implanting and 25% chance of leading to a live birth, and you can find various stats on how many rounds (i.e. egg collections and transfer of all embryos) it will likely take you. This meant that when my first and second transfers didn't work, I was sad but not distraught because, statistically, i expected it. My third transfer is coming up and we have a PGT-A tested 5AA embryo, which means a 70% chance of pregnancy and I know that if this one fails, it will be a lot harder to deal with because of the numbers.
I'd also gently suggest managing expectations around three children. Not that it's impossible, but I have found it easier if I have some flexibility and can go with the flow with this process. We wanted two but I can now also visualise a happy life with one or even none, and that gives me some resilience.
On the whole, it can feel like a long slog but it is manageable. Good luck!