L.,
It is different for every woman, but if your symptoms are severe enough to be disruptive and concerning, I would urge you to talk to your doctor. There may be a better option for you, or it may get better as you body adjusts to the hormones. Here's my experience:
I had my Mirena put in on Dec 3rd & I had HORRIBLE mood swings the first 6 weeks (I am also nursing my son). I would cry at the drop if a hat, feel depressed and snap at the kids for no reason - my 5-year-old actually asked me what was wrong one day while I was folding laundry & when I told her nothing, she asked me why I looked mad! When I talked to my OB/GYN, he said it is unusual, but not unheard of for women to have this severe of a reaction. Apparently my body was just super-sensitive to the Progesterone.
He gave me the option of removal, but since we were using it not only for BC, but to control heavy, irregular (no longer than 10 days between, lasting for 12-20 days) cycles, we decided to give it until April before we made that call. He also told me that if it got any worse to call him immediately and we would remove it and try a different route. (My husband was also supportive of this decision and he just gently points out when I am getting irritable with the kids and offers to take over when he thinks I need a break - this has helped a lot.) Also, just be aware that this is not your fault, it is your body adjusting to the new hormone levels and it will improve as your body adjusts. It helped me to just realize it was happening and make a conscious effort to not let it effect me - it still did, but not as severely.
2 months later, I am happy to say that the mood swings have gotten much less severe - I am back to my normal monthly irritability (that's a whole other issue that was there before the Mirena). Now if I can only get the breakthru bleeding (spotting) under control, it would be great - but they only way for that to subside is time or BC pills & since I am still nursing, the BC pills are not an option, so I just have to hang in there until my son weans.
Good-Luck & hang in there!
~ B.
Mommy to Michaela (7), Sarah (5), & Mickey (17 mos)