Your tax expectations would be that you need to report anything that you sell within a certain tax year. Also, if you have any stocks that pay dividends, that also needs to be reported but if you are trading otc I doubt you have to worry about reporting cash dividends. So anything you sell within the year is a short term gain and you are taxed according to what your personal tax rate is. Long term - if you hold something over a year would be taxed lower - anywhere fro 0-20%.
My personal opinion is if you are "holding too many companies" it means you are stuck in some and never took your losses and went on to the next one. Especially with otc's - most of them are not investments. Learn how to take losses early and when they are still small. That is more important then exiting when you are ahead.