What’s up with salad??

I’ve done nothing but eat crap for months! I’ve gained back every pound lost and more. I weigh the most I ever have. So Monday I started “watching what I’m eating” (code word for the dieting word I hate). I started tracking etc. this am i has to get blood work done so I didn’t eat anything till like 11 and I got a salad at the grocery store I was at. My stomach has been upset all day! So my body is literally in anarchy after two days of eating well? What have I become?? On an up note, i like a challenge so I might eat a salad tomorrow too!