No, you get taxed only once on capital gain income. Short-term gain is taxed the same as other income, long-term (over one year holding period) taxed at a lower rate.
Example
Wages: $30,000
Short-term capital gain: $10,000
Adjusted gross income: $40,000 (total of above)
Deductions: $15,000 (includes 2% deductions after limitation)
Exemptions: $3650
Taxable income ($40,000 - 15,000 - 3650): $21,350
Tax would be the same as if wages were $40,000 and there were no capital gain. But if capital gain were long-term, tax would be lower.
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