How can I get my wife to take interest in our sex life?

Two words: Romance her. It might not work but it's worth a try.

But living with your mother? That's gotta be a turn-off for her, even if they get along very well. Inhibiting. I understand that sometimes it's necessary to share accommodation for a while but if you can get away on your own things might sort themselves out.

If you are already helping around the house with chores, and kids if you have them, so she isn't exhausted at the end of the day, and you are still showing affection without the sexual component, There are a couple of options. Take her out for some alone time where it is just you two and make no mention of the daily drudgery of chores and bills.

If that doesn't work suggest she a doctor. Sometimes it is a medical problem.

Everyone else's answers are awesome .. But if all else fails fermented grapes help . Otherwise known as wine.

First, You mentioned a time measure like once in two week . .You need to remember,  physical contact doesn't have a measure, only you do it when you are ready physically & psychologically. Marriage & also being in young ages period, doesn't mean physical contact needs to be overreacted. There might be several factors you need reconsider. A little wrong move in these majors would destroy the whole relationship. 

As a man, you are the provider & your wife's will & feelings are the priority. It's important to remember, never press her toward your needs. If she doesn't feel like it, you need to respect that. This is part of marriage.  What I think is, she is interested already, but not feeling like it. These are different.  It could be the effect of her menstrual cycles & her job & also her tiredness or maybe the environment is not comfortable for her.  I don't know how you're looking at the point & how you applying through this. But you need to walk with her feelings.  When she doesn't feel like it,  you shouldn't sound pushy. You need to find her comfort zones. You need to help her more, be around her more, be closer to her, be more romantic, be kind, listen to her well, give her attention as well & show your love strongly. Make compliments about her appearance, when she make very simple changes, you need to notice & express it  Surprise her with gifts. 

All these things would be exciting foe her, & being excited with her husband can actively produce pleasuring hormones which would prepare her for further joy. Or above all that, maybe you are doing wrong in your duty, maybe you are not providing her needs  You should know that you need to always follow her guide. Maybe you need to gain your sexual knowledge more.  Maybe she's not satisfied as well as she expects & feels.  Maybe she's stressed out to tell you as well be cause she might think she would disappoint you.That would depends how truly you build your relationship close & comfortable. There are so many many things to consider . .since I don't know what situation you dealing with, I can only speak my mind & guesses randomly & that can take forever!

I think you ought to make plans to be independent of her mother and have your own place, and I think this should happen soon before non-interest in sex becomes an entrenched pattern 

In the meantime, go for weekends in hotels in another community.  Get away and get a room with a jacuzzi.  You be the one to order champagne and bath oil.  Have dinner sent to your room.  Concentrate only upon her sexual pleasure.

This is really simple. If you want your wife to partake in more sexual activities with you, then give her a reason to want to.  Chances are this isn't because of your wife but has more to do with you via your actions and/or attitude towards her, so do some soul searching here and see if there isn't something you cant change to put her more in the mood for more.  

Just like when I played Pro-Football many years ago as a QB, I was told that if I wanted my receivers to catch more than give them something more to catch so hope this makes sense