30 y/o m, just got over severe pneumonia, now has what seems to be sinus infection ever since. could they be linked?

Yes: Sinus congestion can linger after pneumonia. It usually starts with a viral infection and then the sinuses get blocked causing pressure. You can try saline nasal washes to open the sinus passages and promote drainage.

Definitely: Serious pneumonias can sometimes wreak havoc on the same defenses that protect you from sinus infections (like the damage caused by hurricane katrina hitting the gulf coast)- the extent of damage may takes months or more to recover from. Rarely, the damage imay contribute to developing something called cvid- a vaccine challenge test can be done by an id or allergy doctor to diagnose it.