I hate to say it but it's really allergies folks.  Food u can have reactions to include sinus drain. Start by taking one at a time out of your routine.

our bodies n gut change over time.  Our food is full of chemicals n as we age our gut becomes unbalanced.  Get a good probiotic n a gut biome balancing supplement to rid yourself of bad bacteria.  A lot of allergies will improve.  Educate yourself on th immune system.  All skin rashes n allergy symptoms start n end here.  With gut unbalance you migh get hypothyroid.  Have it checked.  Th six in depth testing.  Plain TSH doesn't help.  This affects the liver too.  Also cholesterol.  Avoid statins n learn about healthy thyroid meals n snacks.  Eat organic.

lastly get a good sinus spray n use it every day.  Get a mister fr inside th house.  All head symptoms contribute to th drainage unfortunately so adding a natural homeopathic helper like mullein will do wonders to thin th mucos.  Stay away from meds that just dry up drainage.  Homeopathic is always better and infinitely cheaper.  Usually we only just improve as we age but never return to that before stage.  The above steps really help it though.  Try not to sleep flat and get a good HEPA filter for the bedroom.  One for down/upstairs too if possible.  Don't forget to check around for mold too.  Our bodies hate it.

Good Luck n God Bless to everyone in the Allergy fight