I am lifting very heavy, trying to gain mass. I am trying to eat enough calories a day to supplement my caloric intake.

I am getting bigger, (not alot, but noticable enough) but i am also getting a bit of a gut (ok more than a bit)

So, i started doing 30 minutes of low impact cardio at the end of my weight training, doing a heart rate of 116 to 126.

now i have some cuts, but i feel like i loose size after doing cardio. it might be my imagination or it might just be the muscles losing their pump, but what i need to know is, is it harming me to do fat burning cardio after my heavy weight workout?

i have read article that say dont and articles that say it does not make any differance if you keep the heart rate low enough? what should i do

i am 42, 5,8 190lbs

Thanks for any advice