I wouldn't take a chance and would at least call the doctor's office.
There have been a lot of posts recently about IUDs and the side effects. I work with a lady who has developed diabetes as a result of her IUD - the hormones were enough to throw her glucose levels off balance.
You have 2 children who need you. The cost of a doctor's visit is worth learning if there is something wrong. I don't want to scare you, but when my daughter was 7 weeks old, I found a spot on my shoulder that most people thought was nothing - ended-up being cancer. If I had waited, my prognosis would have been much worse.
Most doctor's offices will work with you on payment and may prorate costs based upon income levels.
Just because a side effect is not reported doesn't mean it isn't from the IUD. The FDA requires all pharmaceutical companies and medical device manufacturers to report such information by law. I used to sell a product that received a warning for a side effect that only happened after the drug had been on the market for 4 years - never reported during the clinical trials.