Sex problems

I need to vent ladies, I have been married for 7 years to this amazing husband , he is everything I need , perfect husband and father , I am not even exaggerating lol literally for me he is the perfect man. But after 7 years and a 1 year old I feel like something is missing and I have no idea what it is. We have been having a lot of problems lately especially me with sex I am just never on the mood and I feel bad for him and everytime he even mentions anything I get pissed off I don’t know what to do and don’t know what it is that is making me so sensitive towards the whole having sex issue. I want our relationship to keep going strong as it is and I feel like this whole sex thing is affecting it. Any ideas what could it be ?is it mentally, is it from being to tired with the baby, is there any possibility that our relationship is starting to wear out . How can I spice things up?