For me sunlight and some light exercise everyday were a game changer. I had tried Vitamin D supplements (1000 IU daily) before but there was barely any noticable effect.
1000 is actually way below what you need probably, my doc put me on 2500 a day and it wasn't enough, I've moved to 5000 and been "normal" level ever since for several years for my annual checkout/blood/urine tests. If you have brown/black skin it can be even more, but better to start low and figure out what is enough under observation of a doctor.