best supplement for sperm health

After trying to conceive for a good 18months. I've had a test and my sperm isn't as good as it should be although not totally useless.    Are there any supplements you recommend. 
I've lost 2 stone. Cut right back on my alcohol consumption. Been exercising regular.     
I've heard a lot of names of supplements thrown about such as pre seed etc. 
Just wondering if anyone got any first hand experience of any of these.