The podiatrist did say that a contributory factor can be the development of the calf muscles through, for example, walking. If you do it without stretching exercises, the tendons become over-taut. Presumably Voltarol contains anti-inflammatory stuff?
Voltarol is a brand name for Diclofenac, an NSAID (non-steroidal ant-inflamatory drug). Have a look at getting taped by a physio too, they use kinaeseology tape, which promotes blood flow and healing. Speak nicely and they will show you how to do it yourself (or just look at YouTube and have a go)
I think the key thing in your situation is to remember that you will not be able to walk this off. It will get only worse.
I would suggest that you rest up and don't sweat the LEJOG. You have three months before the walk you say, so I would rest up and try to recover it. You can walk into fitness, you simply cannot walk an Achilles better. Simple as that I am afraid.