No one is really sure what causes ovulation pain. A few theories are that the extra fluid, released when the follicle ruptures releasing the egg, causes some irritation, leading to the pain.. Another theory is that the sharp, sudden pain may be caused by the egg itself due to bursting out from the follicle. Spasms of the fallopian tubes or uterus as ovulation approaches may result in this pain.
While ovulation pain is common, severe pain
around ovulation should be checked out, especially if you're taking fertility
drugs or it can also be a symptom of endometriosis
or pelvic inflammatory disease
Severe stomach pain that comes during or just after ovulation, while taking fertility drugs, could be ovarian hyperstimulation syndrome
I don't think mirena coil is the cause for your ovulation pain.
Do consult your doctor to look for any pathological cause,if any.