First of all...the size of penis is determined genetically & it won't grow after a certain limit
And the medications like Sildenafil
citrate (Viagra) maintains erection by increasing blood flow to the penis.
Performance can be improved by having a diet rich in fruits, vegetables, fish, nuts & honey.
You can also do oil massage
of the penis...it increases blood flow & maintains the erection.
One more thing...avoid consuming any over the counter medication
which claim to increase the size or improve performance...it may be harmful.
Best thing is to eat a healthy diet, exercise regularly, avoid stress
, get good sleep, think positive and stay happy.
Wishing you Good Health.
Thanks and take care.