to run or not to run??

I have been training for a half marathon that is TOMORROW morning!! Before I started training for the 1/2 mary, I was training for my tris, a duathlon, and a 10M run. However, over the last two weeks I've been noticing some pain in my left ankle around the bone...maybe in the joint area. It never hurt while I was running, just after. I would take Ibuprofen and ice it and it would go away. Well, this past week I ran on Wed. and immediately after my run my ankle was killing me. The pain was worse than ever before and it still hurt when I went to bed. Thurs...still ankle pain. Friday, I was going to run but decided against it b/c my ankle was still bothering me and I actually started limping a little bit by the end of the day. I iced it and took ibu. throughout the day. Today it's still pretty painful, but not as bad as yesterday. I'm not sure what's going on with my ankle, but it's definitely something!

My question is: do I try to run my half marathon tomorrow or skip it? My concern is that I could have something really wrong with my ankle and running tomorrow will make it significantly worse. Or, I start running and 3 miles into it I can barely walk. I feel like I have trained so hard for this and I am just so disappointed in knowing that I may not be able to run tomorrow. But, I don't want to make a problem bad beyond repair that would inhibit me from racing in the future! What should I do?

Also, I have had a gait analysis done...so I know I'm in the right shoes. I don't feel like I put in too many miles too fast because I followed a pretty strict plan (Hal Higdon's) and I was already at the 10M mark in September. So basically I've just been building up my miles for the 1/2 mary. And I'm not sure if this matters, but I'm 32 and weigh about 120...so I don't think weight is an issue either.

Any input/advice would be greatly appreciated!! Thanks!