First Line TX or Second Line TX

I will be starting my FNP program in a couple of months and I have been pre-reading my pharmacotherapeutic textbook. So.... I apologize ahead of time if my question seems a bit basic.

I have a question on what is the best practice in prescribing meds to a new patient who has already tried an OTC equivalent to what a NP would normally prescribe as a first line tx.

Generally speaking, do you start with a different first line tx or do you immediately try a second line tx since a first line tx has already been tried?

For example if a new pt comes to you with symptoms of poison ivy and has already tried otc's including hydrocortisone, would I go ahead a start prescribing a different first line corticosteroid or would I try an intermediate corticosteroid first?

Or, if a new pt comes to you with symptoms of a tension headache and has already tried other otc first line tx's....do I try other first line tx's first before preceding to a second line tx?

The way the questions are asked at the end of the chapters tend to lead me to think I should always start with a 1st line tx. Maybe I'm making it a more confusing than it needs to be....But with the poison ivy example I chose to start with an intermediate corticosteroid first until symptoms resolve and then change to a lower potency corticosteroid, not to exceed 14 days with the combo. Why would I start with a first line tx when the patient has already tried a first line tx unsuccessfully? The only reason I can think of is that I don't know if the patient used the first line tx correctly or applied enough applications. But anyway, like I said maybe I am over analyzing it a bit?