I’ve been having some real issues lately with regards to ischial tuberosity pain when riding on both my XC FS (M) and hardtail (L). I’m 6 foot. I’ve had two bike fits, one a traditional fit and the other with the fancy pressure mapping and sensors. They ended up putting a wider saddle, raising the seat and a bit longer stem on my FS which was at the fancier fit. The pain seems to happen a few miles in, can get worse with climbing especially on longer fire road type climbs. Typically starts on both sides but favors my right. Sometimes it goes away for a bit on the ride but comes back and usually after the ride I have pain in that area with skin irritation and also pain that will radiate into the hamstrings. I use chamois cream, bibs are new and always clean. I’m really getting frustrated at this point. I do have some back issues on the right but they have been around for years. I thought it was due to the medium FS but this is also happening on my large frame. I’ve tried multiple saddles, thick and thin. The thicker seemed to help but it happened this weekend again climbing steeper fire roads and again I have irritation of the skin in the gluteal folds. I’ve messed with the saddle height on both, tilt etc. Again sometimes it will help but tends to come back.
Hey!! Welcome to the forum!
That sounds very frustrating. Nothing worse than pain interfering with something that should bring you joy 
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Getting a bike fit (or 2) was a great start. Have you been to a physiotherapist? If not, I would suggest this be your next step. It could be that there is a muscular imbalance or weakness somewhere that is causing you to adopt a sub-optimal position (even if very slight) on the bike to cause downstream issues.
I hope you find a solution soon! 
Thank you! No, I have not but its on the list. I wanted to rule out anything bike related first but I’m starting to think its my body rather than a component.
I had something similar years ago, turned out to be ischial bursitis. Super tight hamstring and adductor muscles can cause the bursa on your sit bone to flare up. In my case I found out I actually had a short leg on that side and was sitting crooked on the bike. Seeing a doctor for a scan to confirm what’s causing the pain and a bike fit with someone skilled in dealing with pelvic asymmetry (if that’sthe cause) would be a good start. Good luck!
Did you happen to get recommendations for exercises or was it purely shims and components getting swapped out?
I use a combination of cleat shims and cleat wedges plus G8 2620 insoles. Off the bike I have a mobility routine I go through every morning and evening involving stretching, foam roller, and a tennis ball to target trigger points in order to keep my body loose and limber. A manual therapist like a Rolfer or chiropractor who is trained in Active Release Technique can help get your body straightened out to start with. I used the self help section on Steve Hogg’s bike fitting website to work out how to fix myself since I don’t have any qualified fitters near me, but it’s a constant work in progress. I wasted a lot of money on fitters who never even noticed I had a leg length discrepancy.
I’m no fitting expert but my first fit missed a leg length discrepancy which seemed to be the cause of any problems I had. It might be correct for you but I’d question raising the saddle, my understanding it’ll take some of the load of the legs but that will transfer to your rear, and the higher saddle will also strain the back of you legs. But as I said I’m no fitting expert. Good luck!
Thanks! Ya the last fit I did which was highly recommended and pricey thought I had a shorter right leg but then put me into a different position on a table and said no doesn’t look like it. It’s strange though I definitely can tell a difference in the length and a colleague of mine, I work in medicine, examined me and said it was shorter.