Ean your best chance will be to start some eccentric soleus loading (3 x 15 reps twice a day every day) as soon as possible, I had similar problem though not as severe and pretty much dissappeared after a couple of weeks, but it depends how long this has been lurking in the background.
Also do some deep tissue massage every day for a few minutes, with your thumb and index finger either side of the achilles, in circular motions directly over the painful area
You will need to cross train for a few days to just give this chance
I am a Physio and yes there is light at the end of the tunnel!..you can most definately make a full recovery and get back to running.
Dont be surprised if your GP is reluctant to refer you for an MRI, these are usually reserved for patients with worsening neurological symptoms who need urgent surgery and not recovering sciatica..unfortunately when people know they have disc or joint pathology they often become more focused on their 'damaged' backs..this can lead to the path of gradual deconditioning as people avoid more and more activities
I sympathise sciatica is excruciating but it looks like youre coming out on the better side of it. I think someone else suggestion of yoga or pilates is a good idea, it sounds like you have some residual stiffness from obviously being a little immobile due to the pain! your joints will enjoy a good stretch!
With regards to running..suck it and see..start slow..walk..jog/walk...and build up again gradually. if youre a little bit stiff/sore later or the day after..to be expected..if increase in leg symptoms..its not quite ready to run..but still walking is great!
Hope thats a help
I see people make full recovery all the time, good luck