1) maybe your just getting to excited? How old are you? How long do you spend during foreplay?

If your messing around for an hour etc before sticking you meat in her and haven't came with light touching, playing of your penis then if you cum in a quick time in sex, it may not be regarded as p.E

2) kegal excersise are only recommended for older people, you can do damage to yourself if you are young. Kegal excersise work your love muscle, to test that if its strong enough do this:

when taking a piss, stop pissing, if you can hold off pissing without to much problem and start again, then stop, start, your muscle is strong. If you can't stop and hold it, its weak, therefore you have less control when wanting to cum.

2) wehn you get a boner, stand up and hang a reasonably big towel (one that coevers your body) and if you can take the weight of it then you have a strong love muscle.

tips

use condoms.
Use de-senstising gels
masturbate more frequently
stop start method...Gunna come...Stop...Wait...Start again....
Squeeze method...Gunna come? Squeeze the base of your penis.
Three condoms? Thick ones...?

Hope dat helps.