Does she not want me?

My wife and i have been together for 13 years, lately it has just been a big struggle. My wife just seems to ignore me most of the time i really do try and make things better but the harder i try the worse it gets. I really do love my wife dearly and don't want to lose her.I am not the most perfect man i know we all have our quibbles, my wife has been training to be a nurse for the last 2 years so i understand that she is busy and stressed. Our sex life is non- existent, when i try and make a move i am just turned down, or some excuse is made, i then get in trouble for pestering her for sex cant win i makes me feel so rejected, silly and makes me feel like a perv.. I dont feel like much of a husband right now.My wife will be the bread winner so i feel like i have failed her i stay at home with kids do housework ironing school runs ect.. so i just feel a bit useless. Does anyone have any advice for me thanks.I feel all of the problems are my fault, just dont know what to do or think anymore,