I had the same issue with Cosentyx - the 150 mg dose did not work. The loading doses, when I was taking Cosentyx weekly, worked very well. We were able to up my Cosentyx to 300 mg and that helped a lot.
I did have GI side effects but I also have IBD, so we expected them. I was able to keep the IBD under control with a different medication and so was able to stay on the Cosentyx despite having an IBD flare.
Cosentyx has provided me the most pain relief of all the biologics I've tried (including literally every anti-TNF - Enbrel, Humira, Remicade, Simponi, back to Remicade, Simponi Aria and Cimzia), so I think dealing with the GI side effects were worth it.