Need New Ideas to Developing Algorithm Using Priority Queue

Hi All, I am developing a web scraping algorithm using Priority Queue to enqueue the new parsed links from seed URL to the queue and then dequeue the seed URL from the queue then start to select new seed URL from Priority Queue according to an algorithm i am developing it. The program is running without any problem. But the problem is: - Since (enqueue Links > dequeue), the size of Priority Queue is getting bigger and bigger by the time. How can I control of it ? - When I am try to get number of crawled URLs per minutes, i am getting low results by the time. Ex: after running the program for 1 hour, the average of crawled page is getting low than if i run the program for 15 minutes and get the average of crawled pages. How to fix this? I have these two issues and need your help and your idea to solve this problem in my crawled algorithm. Thanks All