TTC with hypothyroidism

Can anyone give me some advice. On Monday I was diagnosed with slight hypothyroidism. My doctor has put me on levothyroxine 25mg and said for a repeat blood test in two months. I haven't took them yet is there any side effects to them?. My doctor seems to think that it's the reason I am struggling to lose weight and conceive. He said things should go back to normal after I take them is this correct?. I have found myself becoming depressed being a mum is something I've wanted my whole life. My fiance has been super supportive and reassures me everything will be ok.