i look good when i flex, bad when i dont why?

hi, im 20 years old and weigh about 150lbs ive have been working out for a few years but i noticed that when i dont flex my body has a drooping/sagging look to it, my chest has more of a C shape, and my stomach appears bloated, just overall looks bad, but when i flex my body looks so much tighter and better, my abs really appear, i can see all 8, and i have a good dip in the middle (but when i dont flex its rounded as in a barley noticable line down the middle) and when i flex my chest it reshapes into somthing much better and the bottom has a nice horizontal line(connecting both pecs), and honestly when ever i go out to the beach or pool im always flexing and people tell me how cut i am (primarily because i have decent sized muscle for someone who is 150lbs) and im embarassed to not flex because it would look bad. how can i fix this?

I notice that when i flex my body/skin becomes much tighter, do i need to loose weight, tone my muscle for a better (non flexed) shape?


{EDIT by mod: Could you please refrain from adding URLs to gambling sites as they are banned on this site}

You shouldn't be sagging at 20. I'd guess that you may have focussed on decline bench press & or dips which primarily work the lower pecs, you need to focus on incline bench press & drop (for the moment any decline & dipping movements - to be accurate you can do an upright dip as long as you focus on not leaning forwards, this will then work mainly the triceps & shoulders, not the chest so much.
For the stomach I'd work on planks, side planks & shoulder bridge to strengthen the core...but it may be that you're actually carrying some added stomach fat if it is bloating out - & you're not on HGH-which at 20 you shouldn't even be thinking of. Even if you want to go pro you wouldn't need to think about any drugs until you'd at least made national level & hit at least 25 (& to be honest if you are male & 150 pounds you'd need another 30-50 pounds without drugs before you got anywhere on stage).
Basically you need to work out, maybe spend some time adding mass, then go for a cut. If you remember it takes years to add muscle, but weeks to lose fat, then you'll realise that the bulk of your training at your age should be focussed on adding mass. If you can get up to 160-180 pounds (or more if you are tall), then you'll look a whole lot better than a sagging 150 pounds. Even with some fat the bulk of muscle will give you a strong guy look, not a flabby boy look. So plan a 2 stage attack first (assuming you're in the northern hemisphere) take at least the next 6 months to work hard. Hammer those squats & deadlifts, add in incline bench press, shoulder press (unless you are a throwing athlete), work on stability in the core & rotational mobility (yes you can still do some crunches, sit-ups, but don't go crazy focus mainly on stability & rotational power).
A simple beginner workout can be found here (it's a pdf, so you'll need acrobat reader to view it.
Hopefully you'll get on the right track after a few months hammering this routine!

EDIT - Important!
I just read your other post about your BAV condition - before you do anything check with your doctor - you may not be in a position to add much more mass (as more mass can raise arterial pressure) & the routine I suggested was for a healthy 20 year old. You are a special case so do not start anything without talking everything over with your doctor. Ask about gaining lean body mass, how hard can you exercise & what choices you have available. If it seems like he doesn't know then try & get to a physical therapist who has experience with athletes or someone who has worked with clients with your condition & so has some experience. Finally whatever they say if anything you do seems to cause you issues, then back-off or stop that activity whatever anyone says - do not ignore warning signs!