Normal TSH and FT4, low FT3?

I have hypothyroidism. Diagnosed it 2 years ago. Recently it looks like my FT3 fell down (now it is 3.1 pmol/L) . But my TSH and FT4 are normal. My doctor keeps on telling me that my results are normal and FT3 is not important! But I am feeling awful, all the time tired, moody, have apathy to everything. Can't stand it any more. Doctor said that may be I have postpartum depression or may be i am just lazy!! But I am not lazy person, I really feel tiredness:( Depression? may be. But I love my daughter and she is so well behaved baby that she doesn't bring me feeling of hassle. I searched internet and found out that might have problem with conversion of t4 to t3. Any thoughts about my problem? Is it important level of FT3? Can low FT3 be that cause of my condition?