For Example. If l buy 4000 stocks for $0.45 and because of a very volatile situation now l sell them and buy them back several times in a week; sure making profit of them. In this way l will be making at least $300 per day with at least 3-5 transactions per day depending in the volatile the market is each day.
Does this activity in my account may increase my taxes at the end of the year???
Or l will be taxed just for the gains in my account?
l live in Oregon

On your federal taxes your capital gains will be short term and taxed as normal income. Stocks held for longer than one year are considered long term capital gains and are taxed at a much lower rate. The number of transactions has no effect on taxes. It is the length of time you hold each stock that effects your tax rate.

TJ is mostly right, if you hold for less that a year your gains will be taxed as ordinary income.

Do not try to reduce your tax liability by selling stocks that go down and buying them back at a lower price; the wash rule prevents this strategy from working and you will be subject to the same taxes as if you had never made the sale. Also, shorting a stock and then closing the box when it goes down is not a viable tax strategy any more either.