Advice on second child?

Hello. My husband and I have been happily married and had our first child in 2013 he is a wonderful little boy. We have been trying for child two for quite a while now and we have had no luck. What position works best? Should he take Viagra? We are really pushing for this second child. He has no problem pleasing me and I have no problem pleasing him. He enjoys talking and playful "spanking" during intercourse. He also has no issues staying hard without Viagra, he has never had to take it, though I have tried to mix it in with his food sometimes.