It could show you have an infection, inflammation or chronic disease e.g. hypothyroidism not properly medicated.
You could also react quickly to supplementing iron.
Or it could be both.
If you are supplementing iron you need to stop immediately.
The best way to determine if there is any other cause is simply to respond to how do you feel? What is the condition of your skin, hair and nails like?
The Royal Australian College of General Practitioners have published this paper on iron which seems to be quite well thought through. Careful reading might help:
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