there are natural ways to boost your testosterone level.

also, wokring out in the mornings may help as your body has higher testosterone then.

btw, are you resting enough between workouts?
also, eat a lot of red meat and dietary fats (including saturated fats). this has been shown to boost test levels. a lot of carbs too.

i dont have any experience with xyience's xtest, but i have taken tribulus terrestris and tribestin and both have seemed to have helped me gain weight. my friends have taken 6-OXO and have gotten good results with that.