Hi there and

! My DH's volume is better than normal but everything else is awful, go figure! Here are a few supplements that can help with volume:
L-lysine (500 mg/day)
N-acetyl Cysteine (600 mg/day)
L-arginine (2000-4000 grams/day)
Also have your DH drink lots of water, that in itself can improve the volume.
Even if your DH has a normal count per mililter, if his volume is low it could bring the total count down enough to cause an issue. Do you know what his total count is? As far as you going on Clomid, I would ask you doctor about the pros and cons. Hopefully it will improve your chances though.