UnXmas is absolutely right about this being early days still and that the only thing to really worry about in terms of progress is if you were going backwards. Definitely an increase in pain (after stopping your immediate post op pain relief) and getting increasingly tired as time goes on are things that can be a sign that all is not progressing as it should be, as well as fever, as you mentioned, and the inability to keep food down.
But do be reassured that at this stage not having a normal appetite and experiencing a little nausea and lacking energy is very normal.
I know it's especially hard when you have people who need and want you to get back to normal and be able to take care of them and do all those things you normally do but right now you do need extra rest and to not push yourself too hard so that you can make a good recovery.
I know it doesn't feel like it now but there's every reason to believe you'll be okay at the 8 week mark. You may make steady progress over the next few weeks as your gut settles - and guts really do take time to settle down after surgery. It's not just the incision you see on the outside or those on the inside that need to heal but your bowel doesn't like being moved around by the surgeon and it needs time to get back to it's normal rhythm and start working normally after surgery.
I have had a surgery where it felt like I was not making much progress at all and then almost magically at the six week mark I felt all better - better than ever in fact. And that was a big Crohn's surgery with a resection, lots of strictureplasties, many adhesions, an abscess and infection to be drained. I'm hoping that it sounds encouraging to you that I didn't actually walk for 11 days after that surgery because the pain was so bad and had hardly any appetite but six weeks to the day after surgery I asked my surgeon if I could go skiing and he said yes
So yes, I agree with the 6-8 week timeframe. My surgeon talks about 6 weeks being the magic timescale often with abdominal surgery.
About the oral thrush. I suffered with that after my last surgery, I think because my mouth was so dry for so long (and I probably needed to do extra frequent toothbrushing and mouthwash because of that, but didn't), and I did warm salt water mouthwashes three times a day and found that really helped .
Good luck! And keep us updated!