Could be not enough protein.. or just not enough calories in general... What's yer diet like? Typically? If you're 181... and you wanna grow... then your BW x 18 is 3200. x 20 is 3620... so 4000 MIGHT be over kill... but should work... So lets see...
4000 calories @ 50/20/30 is:
500g Protein 200g Carbs 130g Fat
That equals: 3970 calories... PLENTY to grow on... and LOTS of protein...
Here is a 4000 calorie diet with those macros: (plug it all into Fit day, and adjust if you wanna change things around)
Breakfast:
3 scoop(s), 100% Whey Gold Standard
1 cup, Quaker Oats
0.5 cup, Berries
10:00am:
12 Large Whole Egg(s)
1 cup, Spinach (cooked)
0.5oz, Almonds
Lunch:
12oz, Chicken Breast (no skin)
1 cup, Broccoli (raw)
1oz, Almonds
3:30pm:
2 Cans of Tuna
1 stalk(s), Celery (raw)
1 tbsp, Olive Oil
6:00pm (Post workout):
3 scoop(s), 100% Whey Gold Standard
1 Banana(s) (1 medium)
0.5 oz, Raisins
9:00pm:
11oz, Chicken Breast (no skin)
1 cup, Broccoli (raw)
8oz, Sweet Potato (baked)
Totals:
Calories: 3837
Protein: 503
Carbs: 201
Fats: 134
That should do it!