Im not gaining any more weight?

I'm having problems gaining weight. Im 18 years old and I've had a high metabolism my whole life. I lift weights as a hobby. I've been lifting for the past 6 months. I am currently 5 10, 152 Ibs. and when i first started i was 140 Ibs. I put on about 12 pounds of muscle and all of a sudden i just stopped putting on weight. I haven't put on weight in like 2 months. I eat high protein meals mostly chicken. About 4 -5 meals a day. And i think i'm getting enough protein, 150 - 160 grams a day and i drink enough water. And i'm also going up steadily in my lifts. But i'm just not gaining anymore weight! any suggestions?