I have heard of the concept of "getting a heter" to do something that is not ordinarily permitted, but I don't have a good idea of what it means. I am interested in explanations of what this process entails, particularly when the question is big enough that one needs to get a heter "officially."
I would appreciate answers that address some or all of the following:
If someone needs a heter to do something (either something for which heterim are understood as readily available, like using birth control after having two children; shortening the niddah period in order to conceive; or going without hair covering [women] after divorce--or something personal and more unusual), how does one "officially" get a heter to do so?
--Is it simply a matter of getting the go-ahead from anyone with semikha--or must the approval be from the "official" rabbi of one's community? Or must it, moreover, be from an expert in that area of halacha? A rov? A member of a vaad or beis din?... Or, if I find the loophole myself, and see that it applies to me, can I then take advantage of my "heter"?
Also: when petitioning a rov, does one always have to present a catalogue of extenuating circumstances, or in some cases is even the desire for a heter enough to get one? (That is, if I have a son and daughter already, must I have a special reason in order to be eligible to use birth control? ...And if not--if everyone gets one--why bother going to the rov at all?)
Perhaps this question can be best summed up by my own situation, its motivation: I asked my community rabbi a shayla about a personal circumstance. He gave a stunningly lenient answer about what to do. Would it now be correct for me to say I have a "heter" to do such and such according to his advice?