poppiesinaline - write down what is happening with your periods and take it with you to show the GP. Being 36 it is unlikely that the irregularities and problems you have been experiencing are perimenopause (though some women do go through this early) - it may be that you have a thyroid problem which is disrupting your cycle. You really do need to see your GP to get this looked at - there may be a very simple solution. It is easy to put off, I know (been there, done that ) but that volume of loss you describe will make you anaemic as you can't possibly take in enough iron in your diet to make up for what you're losing.
We often compensate and excuse our tiredness for other things, being busy, etc etc, but eventually it makes you feel sooooo drained and it is harder to play catch up then. In answer to your question, I don't think that the mooncup is anything to with your periods being heavier. What is DOES however, is give you a very accurate guide on volume of loss, and as they information on the Mooncup website says that in the average period a woman will lose the equivalent of three mooncupfuls, it is evident that what you are enduring is way beyond the norm.