Husband sperm count

I think my husband has a low sperm count. He wears briefs and I told him they should be changed to boxers but he won't listen. He is 41 yrs old and I am 36. he never had a child. We want to have one, but it's hard. We have been trying for 5 months and nothing. With my son, I conceived within the month I quit birth control. But that was 10yrs ago. Ugh. Just feeling down and don't know what to do. Any suggestions will help. Thank you!