Are there any ways to straighten up a penis that goes down when erected? Thank you.

Peyronies. Sounds like you have something called peyronie's disease. It is scar tissue (plaque) formation along the shaft of the penis that creates abnormal curvature and deformity of the erect penis. If severe enough (unable to perform intercourse), treatment is warranted. Treatments included medical and surgical therapy. You would need to see a urologist to discuss what would be available for you.