Fertile CM using Mirina??

I'm currently on my 2nd Marina Iud and with my first (full 5 years) I never had egg white cervical mucous. After my first one was removed I went on the pill because we are thinking about starting a family in 3/4 years. That wasn't a good fit for me after 6 months so I had another Marina installed 6 weeks ago. This morning I had a lot of EWCM and I'm worried because we had unprotected sex the day before. Is this normal?