I agree with Julie about seeing a doctor and about being assertive in order to get good care. I too have had the experience of being told my problem was emotional ie: my mentrual pain was caused by my poor relationship with my father. This was 45 years ago when medicine didn't know much about endometriosis. I found an ob/gyn who said that he didn't know what was causing the pain but he knew it was real and would help me deal with it. It took years to find out the source (because medicine hadn't caught up on endometriosis) but I felt OK about it because this doctor was empathetic and reassured me that my pain wasn't "in my head." He prescribed something that helped.
The mirena IUD could be at least part of the reason for your increased irritability. PMS is a hormone issue. So it could also be thr result of changes in your body. There may be something that you can take to counteract the hormones' effects. I've seen a lot of new literature on treating PMS.
Wasn't much known about "female problems" 50 years ago. By the time medicine had found some answers and I was having an easier time I went had a hysterectomy. And getting thru menapause was a piece of cake in comparison to years of painful, excessive flow, irregular periods. Just a note to help you know that medicine does make advances and to not give up hope of help.
I also recommend that you try a different brand of tampons and be sure that they have no scent or extras to deal with odor. I have a lot of allergies and they show up with itching.
In my experience using a tampon when there was very little flow irritated my vagina. After the major flow I switched to panty liners. They are not as difficult as full size pads. Just stick them in your panties before putting them on. some are more absorbent then others. Different brands have different ways of sticking them. I preferred the sticky part on the underside of the pad. (no wings)
I recently saw an ad that showed their pads has having a different sort of wing arrangement. If I still had a period I would try them. They looked much easier to use and appeared to be more securely fastened to your panties before putting them on. I tried the style with just one wing on each side and also thought they were a hassle, always sticking to my clothes and/or coming unstuck from the panties. I bought panties with a plastic lined crotch for period days. In part because my periods were so heavy at times I leaked thru 2 tampons and a panty liner. They would also add security if you're concerned about the pad coming loose. You don't have to use the ones with wings that way.
I don't know if they make them anymore but I liked the sponge and the cervical cap. I bought them over the counter. Then when I stopped bc pills and switched to a diaphragm I was really pleased. The diaphragm holds the flow. The somewhat yucky part was removing it and dumping the blood in the toilet but it was worth it to not have to deal with the rest of the choices and there hassles. A positive was that I could have intercource, without a mess, during my period. I don't know if you could be fitted with one while using an IUD.
I hope you find a solution. I know itching and those messy pads are the pits!