Im only 18 and have had this problem for over a year now.
I think i caused this problem by masturbating for extended periods of time and or bending the penis when erect and or achieving orgasm by grinding my flaccid penis against a pillow or object.
I think i have created scar tissue in my unit, but i am not 100% sure as sometimes my penis feels fine and completely soft, yet sometimes its extremely hard when flaccid and feels tense.
I find it almost impossible to get an erection standing up, however its OK when I’m sitting down in my computer chair position and watching erotic material. But my erection will always die quickly if i don’t continue CONSTANT stimulation when masturbating, it will then return to a hard flaccid state, then eventually a little softer.
I’ve started taking L-Carnitine, Vitamin E, and Vitamin C in an attempt to repair any damaged tissue/vessels in the penis. I have also just bought some 5-HTP as it’s said to correct Serotonin levels IF they are imbalanced.
The condition improves if i don’t masturbate for a few days, however it gets worse if i stop masturbating for too long.
What on earth is going on, i just want this all to end 
ANSWER
Yes, through the bending you may have damaged both your corpus spongiosum and supporting ligaments at the base. Such traumas will promote blood flow abnormalities. Also, the damaged corpus spongiosum won’t be able to properly seal off the penis, so a constant stimulation may be needed to support the erection. There is a possibility that you can’t support erection in an upright position through the lack of proper androgens levels to support both your lower body and proper erectile functioning.
Such traumas should heal over time if properly addressed. There are several agents that will better sexual functions and are responsible for penile tissue health and integrity. A combination of Multi-Alpha, Alpha-Amino, Alpha-AGH, and Ultra-Purified FishOil will promote high androgen hormones and elasticity prostaglandin E1 E3 and Nitric Oxide for healing.
Testicle cooling will prove beneficial in supporting heightened androgens levels.
Also, the SR-Cream should be applied to additionally address the issue as well as possible, so if there are any internal mild hematomas or collagen scar tissue, they will be dissolved.
You will also benefit from hot wraps and baths.
Glad if I could help!