I had gastric bypass 5 years and now I'm having trouble with iron. But that's because my surgeon told me not to take it. Whether or not I absorb it, time will tell. Some of us never will and we'll always need iron infusions. How much and what form of iron have you been taking? Some forms are terrible and useless for us. And amounts, we need lots of the good stuff.
Your B12 and Vitamin D is REALLY bad. The B12 is flirting with permanent nerve damage. Nevermind what the lab range is, we need our B12 at 1000-2000. I keep mine around 1500. I see you're getting shots. I'd also suggest supplementing with sublingual 5,000mcg of the methylcobalamin form of B12 a day. Methylcobalamin is the active form of B12. Some people do fine on the non-active form, cyanocobalamin, but some don't. Cyanocobalamin is converted to methylcobalamin and much gets lost in the conversion process. You also won't absorb iron well if your B12 is so low and you won't be absorbing calcium if your D is so low. No calcium leads to osteoporosis and with no calcium getting through (remember we need 1500-2000mg of calcium citrate per day post op) it won't take long for that to happen. A couple of years of leeching calcium from your bones -- to keep it circulating in your blood to regulate your heart why is why serum calcium levels are useless indicators of actual calcium intake -- is all it takes. How is your folate and copper levels? Folic acid plays a big role in absorbing iron too, as does copper. Copper should be above 90 and folate should be between 15 and 20, optimally. These guidelines are for us with surgery.
If the doctor gave you a prescription for vitamin D, throw it out. I'm not kidding. It is D2 and even normal people don't absorb it that well. WE don't absorb it AT ALL. It's oil based and we malabsorb oils. Many of us in my support group have been on this merry go round and we know how it ends. Find some dry Vitamin D3 and start taking 50,000IU a day and recheck your level in a month. If you can't recheck it, then take that amount for 3 days a week until you can. You can get toxic, but it really takes quite a bit for us and you need your level above 80 which is going to take some work. Again, I'm not speaking for the folks with a normal gut.
Like me, you got the surgery to be healthy. I'm a bit miffed I ended up here when it was avoidable, and I hope you kinda feel the same way! It's motivation.