Fox is a matchup that you pretty much have to call him out on many of his options to beat him, which is why it's so hard. It would be easier for me to help you if I could see a video of one of your matches, but my bold guess is that you challenge his platform camping too much. You need to be patient and notice how he likes to move on the platforms. I find that most players camping platforms are extremely predictable when switching from platform to platform (from the side to the top one). Try to up air them when they do that and not when they are shielding on the side platforms, because most good Foxes are gonna Shield drop Bair or Shine ou out of it. If you have a good anti platform camping game, the Fox will be forced to actually play the game against you, which is what you want.
So my guess is that the Fox is basically waiting for you to put out a laggy move to go in, which is a good strategy against any matchup. Try to avoid putting out randy F smashes or full jump aerials or stuff like that in an unsafe way, because that's what the Fox will be looking out for. I like to bait the Fox in by using Jabs and AC Bairs because they have very low lag.
When you're getting pressured, you can't do much about it aside from Rolling out or Wavedashing out of Shield to get away. There's no unique solution to a spacie pressure, but rather a solution for every way they try to pressure you. This is still a situation you want to avoid as much as possible. Again, if you have a video of one of your matches I could help you better, but I'm gonna try to help you as best as I can.
So when the Fox is on the ground, you want to stay at about a SHFFL distance away from him, which is pretty much the range to which you can react to any of his approaches. You want to try to make him approach you as much as possible. If the Fox approaches you with SHFFL aerials, you can usually punish the landing lag of the move. If he does full hop aerials, you can beat any of they with Up Tilt or SH AC Uair. Still, be careful about Fox's Full hop crossup Bair. It's the only option I don't like to challenge due to the ridiculous hitbox and low lag It's really hard to deal with a Fox that approaches you with running Shine however, but try to see if he can give you a hint on when he wants to go in (things like WDing back, number of dash dances, etc). What I like to do is try to Jab or Bair his running Shine or try to grab the WD after the Shine since it's more laggy than you would think.
If you get hit by the Shine, DI it away. If you do this, they will have no guaranteed follow-up outside of the stupid Side B out of the Shine, which not many Foxes do anyway.
Oh and by the way, Up Throw --> Up Air is not guaranteed on ICs. You need to DI the Throw howeve, preferable behind Fox, and then you can DJ out of it. If you want to SDI it, upwards is the best option IMO due to the Eric Cartman shape of the ICs.
Outside of that, what you should do is pretty situational. Fighting Fox is hard and requires experience. There's no real solution because every Fox plays the matchup differently, so you really have to beat the player and not just the character IMO. If you have a video of one of your matches, you can reply with it and I could help you even further.
I hope it this helps!
