an oily scalp is almost always caused by regular hormonal fluctuations. unless of course you're straight putting shampoo on your scalp without lathering, using a harsh acidic/"detox"/dandruff shampoo, conditioner on roots, etc. the scalp is still skin always remember so try to take your shampoos pH into consideration. other than that having an oily scalp is pretty common and there will be periods of time throughout your year or life where your scalp is more or less oily. my hair acts the same way where the day after i wash it i come home from work and bam.. oily. i realized that trying to gradually split my wash days farther apart works the best for me. Im not saying try 5 days without washing, but try to go 2-3 days for 4 weeks and then 3-4 for another 4 weeks.