Hi and welcome to the Migraines & Headaches Community.
It sounds like Ball has you pretty well covered. Please keep us updated.
What kind of "injection" did you get? Did they do something with your thecal sac? It really sounds like a post-LumbarPuncture headache.
In that case you have a spinal cerebrospinalfluid-leak that causes intracranial hypotension (too low pressure in your skull). That is why you get better lying down, the hydrostatic pressure in your skull increases.
It can go away on its own but you might need an epidural blood patch. Your prognosis should be good since they should have no problem locating the leak since they know on what level they "poked" you. The blood patch should be done on that same level as close to the leaking site as possible.
The diagnosis should be straight forward. Otherwise it is diagnosed with brain MRI with gadolinium contrast. If the MRI is performed too early after the leaking started it might not show anything. Usually it is better to wait one month before doing it. Still there is a 20% risk it might not show the low pressure even if it is there. On the other hand, if it shows signs of low pressure you definitely have it. And I am not talking about blood pressure here but the pressure inside your skull, just to be clear.
Either way, diagnosis should be pretty straight forward.
You can visit csfleak.org for more information.
In the mean time try to rest and spend as much time as possible lying down.
Best wishes!