I had the copper IUD (first one) placed when I was about 8 weeks postpartum. I spotted/bleed for about a week - enough that I would have considered it a period had I not been breastfeeding still at the time. My first period after having the IUD placed was when I stopped nursing my son (10 months later) and that period was HORRIBLY heavy, crampy, etc. I was miserable. The proceeding months were NO big deal at all. My periods last about 4 days with the first two days being heavy, but that's it. It's hard to know whether my first period with the IUD was so bad because it was my first period in about 1.5 years (9 months of pregnancy and 11 months of nursing) or the IUD, but it's awesome now!
I had an IUD put in last summer and I was spotting for about 2-3 weeks after.
Then my periods were really heavier/painful than usually for about 4 months or so, but then they got a lot lighter.
I just had to get another one put in, becuase my iud got displaced and started to come out. (this was on Friday) and I've been spotting since.
I think its pretty normal unless you have a fever or vomiting or something. If it concerns you I would call your doc, and I would definately recommend doing the follow up check; they might give you something for the pain.