You probably started to notice the bugs about a week after repotting?
If there are bugs in there you need to rinse with soapy water several times as the bugs that have not hatched yet deep in the roots wont be rid of by the first wash most likely... So when you rinse you get all the lil flies living in there... Then when you do it a couple days later you will be going for any eggs that may have been present before and have hatched since, Hopefully getting them before they lay more eggs. 2 or 3 good rinses over a week or 2 I think should take care of the problem. I have also heard of other benficial orgnanisms some people use to get rid of pest like this I believe but I don't know to much about it.