
Back story:
In highschool, exercise was a joke to me, I could stay in shape(and look it too) with minimal effort. Ahh, the invincibility of youth! I also made $1,800 a week, but that's beside the point. I was 5'10, weighing in at 175 and very solid! I had an 8 pack, and nearly endless energy. This energy dwindled after highschool ended(Class of '08), and I dropped to 165 and my 8 dropped to a 6. Not so bad, but I noticed the difference in energy.
2010,
I had maintained decently since highschool, and was holding at 165 and looking alright. Then came my life changing 4 car pileup... I'll avoid repeating the tale of my legal issues that took 2 years to resolve. I sprained my right ankle, tore a few tendons, and have suffered from tendonitis ever since. For a while there, I let this get me down pretty badly... I drank a lot of soda, ate like a pig, and sat on my a-- playing Call of Duty. This led to my highest ever weight of 192...
2011(Fall),
I decided that I was DONE with being overweight, and I made a promise to myself, to never let my body go again. The older you get, the harder it is to get in shape, and I feel this already(at 22 years old).
I did a crash diet for 2 days(zero food, solely to shrink my stomach down, to cause that "full" feeling sooner).
After those 2 days, I started eating green vegetables, fresh fruit, and a little bit of fish. I also took plenty of vitamins, to balance out the parts of my diet that were lacking. I started running 3 days a week, and exercising at a local gym for 4. These overlapped in such a way, that monday and tuesday were "break" days, for my body to recover.
The end result of this was a loss of 52 pounds in 35 days, and seeing visible definition in my core area. I was dedicated though, and I already had a strong background in nutrition, it didn't hurt that I actually ENJOY preparing my own meals.
At 140 pounds, I felt AMAZING. I was light, I was fast, and I was lean. At this point, I decided to go all the way... I wanted to get my body back to where it was in highschool. I worked more beef and pork into my diet, increased my caloric intake from 2,200-2,600 a day to my current 3,400-4,000 a day, and hit the gym harder than ever. I never gave up running, and I actually now run intervals 2 days a week.
After 1 month on my current exercise "plan", I hit my current weight of 165 pounds. I have a 6 pack again, with solid definition. I've done this with VERY little supplement use(I don't overload my body with creatine or protein powders), I predominantly get my protein from canned tuna. It may sound silly, but the protein content is very high, and the cost is pennies compared to protein powder(The one I use, when I actually take it, comes in at $150/month for full dosage) compared to my "tunatein" cost of $15/month.
I've hit the ever popular "wall" in fitness. I've been able to barely squeeze over 170 pounds, for a few days, but unable to hold that weight for long. I'm not shooting for 200 pounds of "oh s---!" here, but it would be nice to see 175 or 180, you know? The only times I've been able to get past 165 in the past year, I had to cut down on running and bump my caloric intake above 5,000 a day. For obvious reasons, that is utterly out of the question.
Do any of you have any suggestions, or experience in this area? I'm looking to maintain that "lean, hard look" while increasing muscle mass slightly. I am not unhappy at my current weight, but it would be nice to put on another 10 pounds of muscle, without sacrificing my speed and flexibility.
Weekly Exercise:
Currently I run about 16 miles a week(counting intervals)
I do yoga twice a week
I strictly follow P90X doubles schedule bi-weekly, offsetting weeks lifting free weights at the gym.
I also have a tuesday/thursday PE course at my local college, which focuses heavily on cardio and core.
All this, coupled with a caloric intake of 3,400-4,000/day, should have gotten me farther than it has. I genuinely don't understand where I'm getting stuck.

Edit:
I forgot to mention, I eat 8 times a day. Roughly every 2 hours, only until my hunger is no longer present. I never eat until "full".