Your Lexapro could be the culprit, but one of my best friends just had her Mirena removed. She had been assured that hormones are local and don't go into the bloodstream. She has a host of medical problems (her mother was prescribed diet pills during her pregnancy with my friend in the '60s), including extreme intolerance to synthetic hormones. For one, she gets debilitating migraines.
Well, she had it inserted about a month ago and was okay for about a week. Then the migraines started, she was moody and she lost her sex drive almost overnight. She has the kind of relationship with her hubby where they have sex at least twice a day (married 10 years; this isn't new for them). She knew it was the Mirena and, over her doctor's protests and insistence that Mirenas don't do this, she had it removed this past Friday.
I'm not saying the Mirena isn't wonderful for an awful lot of women, but some are evidently sensitive to the hormones, IMHO.
Best of luck