Regaining and Increasing Muscle and Weight After Illness!

Hi all, my first time posting on here so thanks for your help beforehand!

I am 19, 5' 11". Before a nasty kidney illness during the last 4 weeks, I was roughly 12.5 stone, with roughly 14% body fat, going to the gym once a week with Thai boxing classes twice a week - 2 weeks into a muscle gain programme with a fairly consistent nutritional diet.

During this time I used MyProtein whey powder and Methoxy-7-Test testosterone boosters from PhD. Both of which I found to work very well.

However, after the illness I am now just under 12 stone. I am fairly well toned but very underweight in muscle and have had many comments on looking too thin - which I agree with naturally.

My question is: How can I gain weight - ideally leaving me at 14 stone after a lengthy programme - whilst retaining good tone (i.e. something resembling a 6 pack!).

I would really like to know if a weight gainer is useful? Being an ex semi-pro footballer I still retain some tone and have strong legs, but would like to bulk up on arms, pecs and chest width.

Your help is really appreciated!! Gaining muscle and losing it so rapidly is down-heartening but hopefully with some guidance you guys could pull me through.

Thanks in advance!!! Tom.