People who have itchy bumps on the scalp that they pick at are hard to treat. Basically, you need to stop scratching, but that's easier for me to say than for you to do.
More important is this: even if you scratch at your scalp, you can't lose hair more than temporarily, because the roots remain. If you're losing hair and it's not growing back, it's almost certainly male-pattern baldness (I assume you're male.) You can't really tell much by looking at your family.
You may be picking at your scalp at least in part because you're upset over your hair loss.
Either way, there isn't any blood test which is likely to shed light on the matter. I suggest you speak to a dermatologist about getting a specific diagnosis. At that point you can consider a course of topical minoxidil or oral Propecia, which is quite helpful at slowing down male hair loss (again, I assume you're male.)
Meantime, do your best not to pick.
Take care.
Dr. Rockoff