Can SIBO cause deficiencies?

I suspect I’ve been battling methane dominant SIBO almost my entire life (I’m 24) and before I came to this conclusion I started taking MiraLAX about 3 months ago for what I only thought was IBS-C. That’s been diagnosed to me since childhood.

For maybe two weeks I felt AMAZING. I was eating like a horse, putting on weight I desperately needed, and literally every aspect of my body health felt 10x better.

Then the bad symptoms slowly came back, even though I had improved my stool frequency from once a week to every day or every other day. This has led me to believe it’s more than that, it’s maybe SIBO. Does this sound about right?

The past month things have gotten worse and I’ve dropped crazy amounts of weight even though my food portions and diet has stayed the same. I went from 168lbs to about 150lbs and now part of my left hand is numb constantly. Google says possible vitamin B12 deficiency from SIBO. None of this has ever happened to me, so did me making my problem more tolerable somehow worsen it over time?

I’ve gone to the doctor and am awaiting a sibo test kit in the mail (it’s been 7 days and they suck at knowing when it’ll be here) but I stopped MiraLAX beforehand in preparation for it and now I’m back to my old problems of course. I can tolerate the constipation but I’m mostly waiting to find out I was right and can get out on the antibiotic regime so I can clear this all out and take something to prevent it from ever coming back.

I’m mostly curious, does this sound like a typical case of SIBO? And how can I explain the weight loss randomly after months of starting daily usage of MiraLAX (17g)?