Trigger Points

The chances are that you do not have tendonitis, but Trigger Points. If so, it's good news because you can treat them yourself.

Trigger points are basically muscle cramps but which are confined to very small areas, and could be in just one or a few muscle fibres.

Because the muscle is tightened, it pulls on the tendons and this can feel like pain, but at the point where the tendon attaches rather than where the tigger point actually is.

I used to get exactly the same problem, feeling like the achilles tendon, and first thing in the morning I could hardly walk. Self-massage cured the problem, see below, while the Dr was saying I needed to rest it for 6 months or maybe even have surgery.

You can treat it by massaging, quite hard, the centre of the calf muscle onto the pointy bit of your other leg's knee cap. When you get the right place, the trigger point, you will feel a small degree of pain, indicating that you have found the trigger point, and then you can repeat the massage. Do the massage for maybe 20 seconds, but repeat it maybe every half hour or so.

You are probably getting trigger points through over use or through dehyrdation, so those drinks with electrolytes may help too.

If you have some spare cash, I recommend this book:
http://www.triggerpointbook.com/plantarf.htm
scroll down to see the bit on the achilles tendon.

p.s.
@BKK Gym - sciatica can actually be trigger points too
http://www.triggerpointbook.com/sciatica.htm