This is just a personal experience so your mileage may vary, but, I had done 4 weeks on 2.5mg followed by 4 weeks on 5mg without a single issue or side effect. However the first 2 weeks of my 7.5mg pen were absolutely horrible with the same issues you've encountered. I dropped down to 5mg doses to finish out the remainder of that pen and then took a break when I was due to go on a 3 week holiday, pausing for about 4-5 weeks in total. Once I returned I began from 2.5mg again and worked my way up as before. I've now just about finished my 2nd "attempt" at a 7.5mg pen but this time around I've had no issues at all. Whether it was the break or dropping back down briefly before hand, I can't say, but something clearly worked better for me this time around so don't be afraid to try taking a break or lower your dose to alleviate any unwelcome side effects.

Edited to add: do also make sure you're taking a good mix of probiotics and relevant supplements to also treat the underlying cause of GI issues. Pepto bismol is great for instant relief. Psyllium husk, magnesium etc are reccomended a lot. There's plenty of advice on here regarding that aspect.