There are online tests but they can't be used to diagnose a person with a mental illness. A visit to a physchologist would be the best way to find out if someone has mental illnesses.
Go to the Hospital! You might also need to see a gastroenterologist to deal with gastro intestinal issues.
Usually (in the UK at least) you first see your local doctor. He or she will refer you for furthers tests, to a hospital or a specialist (consultant), if unable to provide a diagnosis.
There are tests men can take at a doctors office. Various tests are available. Sperm count can be done to see the quantity present in semen (low sperm count can be a sign of disease and infertility). The quality of the semen can also be tested.
You need to see a doctor. It is possible that you have miscarried, but only scans and blood tests will tell for sure.
To see whether you have taken illegal drugs recently.
To see what we can't see.
Once you have correctly solved the switched-paintings challenge, you go to the Forgery Detection Lab in the Museum. You have to complete the tests to get the Supply Room key. (see related question)
You can see your regular doctor or a urologist and take tests for STD and infection.
You should definitely take your son to the doctor to be tested for bipolar disorder. The doctor will most likely do psychological tests to see if he meets the things to qualify.
S.A.T.S are the tests you take in high school to determine what college you will go to, because they check to see if you are smart enough for the school curriculum.
They take regular samples from the rivers ans streams, and run a series of tests to see what contaminants are present.
You may have one of many many different medical problems from being slightly lactose intolerant (butter) to having diabetes or other serious medical issues I recommend you see a doctor and have him do a couple tests to see if you have a serious condition