I've had mirena for about a year now but am experiencing low moods or what i feel are irrational behaviors. could this be a hormonal side effect?

Maybe: It's not common for women to have mood changes because of an IUD, since the dose of systemic hormone is extremely low. Whenever you have mood changes, it is important to look at all possible causes - work stress, relationship stress, lack of exercise, grief or loss, or depression. You can always have the IUD removed to see if your mood improves - but it isn't likely from the IUD.