Tracey, direct answer: this is common, it is very likely the iron and the sleeve together, and it is absolutely a ring-your-team thing rather than a make-peace-with-it thing, mostly because the fix is easy and the version you're describing, once a week and painful, is past the point where fluid and walking alone tend to sort it.
The mechanics, briefly, because they explain why it's hit you now rather than in the first weeks. A sleeve-sized diet produces very little bulk, so going every 2 or 3 days without straining was never constipation, it was just a small intake doing what small intakes do. Oral iron then firms up whatever is there and slows it down, calcium can add to that, and if fluids are even slightly short, which Alan has confessed to on all our behalves, the bowel takes more water out of what's passing through and you get exactly the hard, painful, once-a-week pattern you've got. I had the identical thing when my own iron went up in the first year, and it took me a stupid amount of time to connect a change in a tablet with a change in the bathroom. I wrote up the whole picture in constipation after a gastric sleeve, including the bit about what's normal and what isn't.
What your team can actually do, which the chemist can't: look at the form and timing of the iron, since not every version is equally constipating and some people do far better with it taken differently; decide whether a softener or a gentle osmotic laxative alongside it makes sense for you, chosen for a sleeve rather than grabbed off a shelf, because some products are fizzy or sugary or need more fluid than you're managing; and check that the iron adjustment is still the right one on your next bloods. What they will not do is take you off the iron for the sake of your bowels, and please don't do that yourself either, since the whole reason the vitamins and monitoring routine exists is that deficiency is the bigger risk by a distance.
In the meantime, the three things that shift most cases: actually measure the fluid for a few days and aim for the 1.5 to 2 litre range sipped between meals, get some soft fibre in behind the protein (oats, stewed fruit, pulses, veg with skins where they agree with you) but only with the fluid, never without, and keep walking. And the fear of laxatives with a sleeve: it's the fizz, the sugar, and the big tablets that don't suit a sleeve, not the idea of them. Your team will name one. The things I'd ring about today rather than this week are different: severe or worsening belly pain, vomiting, a tight swollen belly, no wind at all, or blood. Those aren't constipation and they don't wait.