Dull aching in the testicles.

I'm a 17 year old male and for about a week, i've been experiencing some dull aching in my left testicle. It never aches on the right and I've noticed that only on the left side, there are two big veins from the base of my penis going upwards that I havent noticed before the ache. It aches when I lie down or sit, but when I stand, the aches almost gone entirely. Another note, my scrotum has been more.. lose, like that during a hot day, but all the time.

I'm embarrassed to go to the doctor. Is this something thats just part of maturing, or is it serious?