My(f19) boyfriend(m23) has a hard time becoming sexually aroused

My boyfriend and I love each other very much and we are always with each other in our spare time. We have never been insanely sexual but always very lovable. (I have always thought my libido was low. Only liking sexual stuff a few days a week) we are always hugging and kissing and holding. Today we had a talk after we fooled around for the first time in a week and he montioned that lately he's been even less aroused by many things that normally would get him excited. (He says he is definitely still attracted to me and still enjoys when we do things. He was very clear on that).

Both he and I are stressed and tired from work when we get home and we don't always have the same schedules. It's hard to make time to be sexual. And let's face it, when you do, it isn't as good as when its spontaneous.

Lately his stress has increased. He's been more exhausted. He's lost a lot of his sex drive. And he is coughing up brown mucous every morning ( been going on for about 3 weeks). I told him to see a doctor but he wants to wait a little longer to go.

Tl:Dr my boyfriends libido has dropped lower. We are both concerned and don't want this to become an issue.

What can I/we do to help boost both of our libidos? And what do you think could be a reason for his sudden issues? Has something similar ever happened to you?