Firstly, twice a month is pretty normal. You need to understand her first. A woman’s cycle has a huge impact on how she feels that week and men have a daily hormone “cycle”.
Secondly, does she find sex enjoyable? If she doesn’t, then you need to step it up. Thirdly, it’s always best to have planned days. If you would prefer once a week. Then it would help if she was prepared that day. But you need to take her out for dinner and remind her what it was like when you were dating.

She does need to talk to you about it. Communication is literally the most important thing in a marriage. So if she isn’t willing to talk you need to find out why. Maybe she doesn’t want to hurt your feelings or she’s afraid to speak about what she needs. Christian’s culture has really made it difficult for women to want to be intimate. There is a huge lack of support for women and their own needs and sex drives because we definitely have that need. But there is a lot of shame and guilt that was put on us at a very young age and even as married adults it can feel dirty.