I have an IUD how possible is it to be pregnant? I am feeling lots of flutters but just had a period

Unlikely. Unlikely but not impossible; all contraceptive methods can fail. If the iud is securely in place (they can slip or migrate) the chance of pregnancy is very low, iud has one of the lowest failure rates for reversible contraception. If you just had a reliable menstrual period, pregnancy is also unlikely. A pregnancy test is still the only reliable way to know.