IUD strings

So last May I had the Mirena put in for the second time.  No problems except on day I couldn't find my stings so I saw my OB who said that they were there, just shorter now.  She said everything was fine and sent me on my way.  Just yesterday checked cervix and suddenly I can feel my stings and they were pretty long considering I haven't felt them in months.  I am due to ovulate and I didn't feel any hard plastic.  I am spotting a bit which is making me nervous because my husband and I did have sex about a week ago.  I know the obvious is to see my OB but I'm just interested in similar stories.  Can the strings get longer and shorter throughout your cycle?