I'm looking to gain and retain a good 5-8lbs.
I'm 28
158-160lbs
5'10
10-12% bf.

Over the past 6 month's I cut down from 186lbs to 158. I've been trying to gain more muscle mass as lean as possible. My diet was been following the clean bulking diet from this forum (I forget the author) roughly 3300 cal per day. I've been doing this for more than 5 weeks and I will slide up to 160 and back down to 158.
My workouts I feel like have plateaued as well. I'm struggling to move up in weight in my squats past 335, bench press past 265, dead lifts past 360 etc.. I have not tried any supplements outside of my whey protein and multi-vitamin. The diet alone has cost a lot and i didn't want to throw any more cash out the window.

My diet has been:
6am : 7 egg whites
1c oatmeal plain

9am: 1.5 scoop whey protein
apple,banana or berries

11am: 8oz Chicken
3/4c brown rice

2pm: 4-6oz Tuna/Chicken
1/2c raw green veggies

4-5pm: pwo 1.5 whey protein

6pm: Chicken/Lean beef
Tons of greens/spinach

9pm: 1scoop protein/fat free yogurt (sometimes)

1-1.5 gallons of water a day.
I'm also lactose intolerant so I take in hardly any dairy if I can help it.
What am I messing up here? I feel like I'm wasting my time and money and I'm getting frustrated. Thanks in advance guys

Joseph