There is certainly controversy on this subject. Many people take the view that personality disorders are only extreme versions of regular personality types. If you can get the book. "A Personality Self Portrait" by John Oldham, he explains this view well.
Psychiatrists are naturally going to have some tendency to "medicalize" various psychological symptoms as they are medical doctors. For instance, if you avoid social relations, a psychiatrist will label you as social phobic, avoidant or schizoid, depending on what other symptoms you might present. However, some people might just be "loners" and that is just how they are. And not likely to change.
What might be most important is how the personality traits that you have affect your life. To what degree are they impairing your ability to function, to have the job or career that you want, to live the life that you want to live? If you are indeed schizoid, you may not have many desires and be quite content with a simple life as long as you can live it alone. In that case, since it is a difficult thing to actually change one's personality, you may just want to get on with your life. On the other hand, if your symptoms cause you distress, you may want to seek treatment, both social phobia and OCD seem to respond well to simple treatment. Schizoid, being more of a core personality, is less likely to change.
"... my question is whether or not disorders such as the ones I have been diagnosed with can be medically detected or if they are merely constructs of psychiatry. as far as I understand, personality disorders are just constructs."
Well, they are constructs in a way, as far as being concepts about personalities. But it might be better to look at them as generalities about certain extreme personality types that are true to the degree that certain people actually have those groups of "traits". Some might have all of the traits to fit a certain category. Others might have 3 or 4 traits. So they are general classes in which certain people fit more or less well, but should not be considered a portrait of any particular person or a definition of. Even at our worse, we are far more than any dis orders we suffer from.
Gary