Especially since this has been going on for a couple weeks ..... #1. Go to a sports Dr!! ... #2. Get your bicycle fit checked!!
In early 2002, my Achilles tendons were bothering me a bit, but I just kept riding. Some days were better, some days were worse. Finally, I did a rather long cycling event in July 2002 .... and both ended up torn.
It was a good 6 months before they started feeling some better ... and I still wear ankle braces on longer and/or hilly rides.
In my case it was a combination of two things:
1) My saddle was too high.
2) I was coming off a three month injury (I burned my left foot to the bone) and because I wanted to do this event later in the summer, I progressed with my training rather aggressively.
Get your situation checked before it gets any worse!!