Iron replacement is extremely complex and I would strongly advise speaking at least in the first instance to a GP about it, although if they aren't able to help you with your symptoms referal to a specialist would likely be more helpful. (If you got your supplements from a GP then if they haven't improved things after 3 months of taking them, that's the time to go back and ask for that specialist referal.)
Oral iron supplements and dietary changes are often of limited use: The gut isn't particularly efficient at absorbing dietary iron picking up at best 10% of what you take in - add in supplements on top and that efficiency gets even worse. What's more flooding your gut with iron can trigger an increase in your hepcidin levels, reducing absorbtion, reducing available iron and generally making things much worse.
If you're taking over the counter supplements without a prescription and are struggling to speak to your GP, while you wait (and you should keep trying to get an appointment) try swapping to taking the supplements every other day rather than daily. This gives your hepcidin levels more of a chance to go down between doses, meaning when you do take the supplement you are likely to absorb more of it. Once you've seen your GP take what they prescribe as they prescribe it and don't be tempted to take any additional supplements containing iron as they will just make things worse.
Good luck.