Its likely that not all the tests have been done for both of you as a couple (people who state this more often than not find that the tests below have not all been done). Or its been the bare minimum in terms of a blood test for you and a semen analysis for him (one such sample is not sufficient). They have missed something here and its preventing conception. At three years of ttc without success there is likely to be a problem with either one of you or with both of you equally contributing to the subfertility.
Unexplained is no diagnosis at all; all this means is that they have failed to find out what is wrong. Sometimes it is a "diagnosis" given to couples when they have not been adequately investigated. Do not ever accept being told that you are unexplained!.
The most common tests that tend to be omitted are:-
Adequate x-rays of the uterus which may show abnormalities not otherwise seen at laparoscopy.
Hysteroscopy - telescope inspection of the inside of the uterus which may occasionally show abnormalities not seen otherwise
Repeated sperm counts over several weeks and months to make sure there is no subtle abnormality
Testing the sperm in special media such as swim up tests and velocity testing. However, when they are done, they often uncover a hidden cause for the supposed unexplained problem
Thorough hormone tests to detect abnormalities of male hormone or early falls in progesterone
Scanning of the ovaries to see if follicles really are developing and there are no sign of polycystic ovaries.
At the very least ensure that all the above tests have been done and completed within the last six months (any test result over 6 months should be discounted. Both of you need up to date test results).