You are getting recurring dandruff because of harmonal changes in your age...it's because of seborrhoea. You need to wash your hairs more frequently with anti dandruff shampoo and you need to continue that. Your dermatologist may add some sebostatic drug fir you.
Next Steps
Kindly visit any qualified dermatologist and get expert treatment
Health Tips
Don't use hair oil at all...and even if u want to apply hair oil, then apply a bit only on the hairs and not on the scalp.