Something similar happened to me but without vomiting. I wondered about SIBO at first. Once I doubled fluids, ate simpler, and took miralax to get things moving it cleared up fast enough that I didn't worry much. All I use is reta plus some oral supplements like TMG, HMB and epicatechin, so I doubt those caused it. For the welts, pinning straight down gave me bruises. Switching to holding the syringe like a pencil and going in at an angle stopped the bruises right away.
I have to admit I started adding things too fast. Being autistic, peptides and supplements turned into a big obsession for me. My setup has been sterile and I've been precise with doses and mixing. But I'm not feeling right lately. Three months back I began Tirz and it worked great. After that I layered in supplements like Vitamin D, magnesium, fish oil, papaya enzymes, creatine plus a few more. I took fiber now and then when the Tirz effect faded. Then came extra peptides: CJC/ipa, Cagri, KPV, BPC, and a small amount of Reta, introducing one roughly each week. Everything was okay until recently. I also tried a tiny bit of Modafinil for my ongoing tiredness and it cut my afternoon slumps nicely. As mentioned elsewhere, I've developed severe welts at every injection spot. I'm meticulous with peptide handling and site rotation didn't change anything. The odd feeling began the day before my last shot, but I went ahead anyway since I hardly ever