I know you say your eating a lot. But perhaps your concept of a lot is not that much. 6 meals a day with 40% carbs 40% protein and about 20% good fat will do it. Supposedly those trying to gain size and strength like say a “powerlifter” would eat twice their weight in pounds, in grams of protein per day I think. Give that a shot. Also go heavy. Do 3-5 reps on heavier weights. This will increase strength (good for rugby) and probably make you get bigger quickly. Just make sure your using the correct form and when you do lift heavy otherwise you’ll get very little out of it and potentially injure yourself.