Can sinus infection cause tooth infection? Or other way around? Been having headaches and sinus probs. Noticed a tooth abscess while brushing tonight

No. Sinus problems can cause tooth soreness, due to root end proximity. Usually more than one tooth is sore on percussion. But they will not cause a tooth abscess.
Other way around . I think it is the other way around ..Some of our teeth are very close to the floor of the sinuses ..Where the bone there is very thin .. When there is infection in one of those teet(peri apical pathosis) it could spread easly into the sinuses . Especially the premolars and molar teeth .
Both. Most common scenario is tooth infection causing sinus infection when the infected tooth penetrates in the nearby sinus cavity. The other way around is less likely unless the pus from the sinus cavity eats up the wall adjacent to the tooth and gushes in the tooth canal, which is extremely unlikely outcome.
#1tooth infect sinus. A tooth infection can create a longstanding sinus infection vs the other way around. The roots of some upper back molars penetrate the sinus. The two are sometimes separated by just a very thin layer of bone ;/or a tissue sinus membrane. A sinus infection may cause a temp, rarely permanent, toothache, whereas an abscessed tooth can "blow" into the sinus to create a long standing sinus infection.