Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
Without the ability to examine you and obtain a history, I can not tell you what the exact cause of your symptoms is. However I will try to provide you with some useful information.
A headache that is worse in the lying down position and then improves with sitting up is not common. After an epidural injection, one potential cause for headache is when there is inadvertent penetration of the needle into the tissue that contains CSF (the fluid that surrounds the brain and spine), leading to leakage of CSF. However in those cases, the headache is worse on sitting or standing and improves with lying down (spinal headaches, which you refer to above). If your back pain starts in one spots then radiates (shoots or spreads like a bolt) to your chest area, this could potentially be due to a radiculopathy, or irritation of the nerves as they exit the spine, which could theoretically be due to the epidural though to be honest I think this would be very unlikely.
A worrisome cause of headache that worsens when lying down is a tumor in a specific part at the back of the brain, but this would be have been seen on the MRI of the brain that you mention you had.
One potential cause to your headaches is what is termed cervicogenic headache: head pain due to neck muscle tightness or stiffness. In that case, maybe lying down would trigger the muscle strain, leading to headache when you lie down. Cervicogenic headache is diagnosed by clinical information (there is no specific test to diagnose it) and is treated with anti-inflammatories, muscle relaxants, physical therapy and other techniques.
If you have not yet been evaluated by a headache specialist (a neurologist specialized in headache medicine) this would be of benefit to you. Follow up with your doctor is recommended. I really can not comment on whether or not your symptoms could be related to an ENT problem.
Thank you for using the forum I hope you find this information useful good luck.
I'm not a doctor, but to me it all points back to that second injection. I would get a second opinion, seriously. I cannot express the need for second opinions enough, as if we had done this, my son and grandson would still be with us. This is not to scare you, but I have learned the hard way that there are good and bad doctors, and have paid dearly for bad ones. Something is obviously wrong, I also think an ENT specialist is a waste of your time and money. There is absolutely no reason for you to continue suffering like this. Find a new neurologist, transfer your files, and ask the new doctor that if he can't figure out what it is, to refer you to someone who can. I'm thinking your next step would be to see a cardiologist. Don't return to the doctor who did the second injection or anyone affiliated with this doctor, as they may be hiding what they did wrong, and trust me, they do protect each other!!!! Good luck to you.