Slow fibre speeds at peak times.

I have had fibre large for over a year and have been generally happy with it (typically 50 down / 16 up speeds). Over the last few months the speeds in the evening (6-10pm) have dropped to a crawl (typically 6/10). Given the time of day I'm guessing this is a capacity issue. Is it possible to find out if my exchange is congested and are there any plans to up the capacity? As the speed goes back up at other times I must be synced at a higher rate.