Can you handle the truth hurts?
After you get older, have a couple of kids and start climbing the career ladder, biology and other things will naturally cause the frequency to slow down. This to an extent is acceptable, but when you are young, healthy and early into your marriage (3 years), you should still be on a roll. As a man or a woman, you are entitled to and have a need for a sex life and if it is not with your spouse, in time it will be with someone else. At some point, your wife will get tired of you asking and you will get tired of asking. (That is a fact!) Sex is extremely critical to your mental wellbeing and health of your relationship. Unless your mate has a medical condition, you can't convince the average man that you are still into him with no sex. (That's how we are wired.)
There are a lot of things that can be fixed, bad breath, weight gain, working too many hours, poor performance, etc. But, based on what you described and notwithstanding a lot of things, I would say there is a strong possibility she is either cheating and/or she is just not physically into you anymore. This situation does not get better, it can get worst and go on for a long time and just make the both of you miscible. Talk it out, counseling, hormone therapy; a marriage is a precious thing and it is worth doing whatever you have to get it fixed. After you have tried and it is still not working, move on and don't spend years in the misery loop when you could be having fun.
(The truth hurts!)