Thank you for your question.
Penis size cannot be increased with medication. For accurate assessment of size when erect use a tape measure to get exact size rather than a visual assessment. The tape will measure exact length from the base to the tip of the penis. circumference nerds to be measured at the widest part just behind the head (glans).
Sexual satisfaction in your partner is dependent upon many factors. of the penile dimensions, the circumference may be the one that is often said to affect sensation more. The most sensitive part of the vagina is at the entrance about 1 - 2 inches.
if you are still concerned please see a urologist who also specialises in andrology.