unable to achieve full erection? still able to ejaculate during intercourse and masturbation.

my problem is that i have never been able to achieve a full erection,

http://en.wikipedia.org/wiki/File:Erection_Development_V2.jpg

i can get to stage 3, and sometimes stage 4 (without the bent), but i feel that it is not fully erect, since i am able to move my penis without touching it, allowing it to "jump" a little bit.

sometimes my penis would return to flaccid after minutes. sometimes the semi erection hinders me during sex, as it will be hard for me to maintain the "semi" erection if i am lying down and the girl is on top.

i am still able to ejaculate during sex/masturbation

my morning boners are stage 3-4 as well

my pc muscle is strong enough to hold in pisses while urinating

my questions are:

1. how can i achieve stage 6 full erection?

2. what is the average duration of an erection? (the duration of penis being at the state of stage 6)

I've done some research, im thinking it could be related to blood circulation.

3. would having too little blood (or anaemia, not sure if this is the right term) have an effect on your erections? if so, what can i do to maintain healthy blood levels in my body?

4. are there any natural ways/food to to improve my blood circulation to aid my erection?

thank you in advance

j