no there is no way to know if you have anything today. it usually takes a few months before that comes up in your blood work.

like 2 or three months or longer?

depends on the std. usually within a few months... some can take up to 6 months... and others can take longer. if you're female, i would recommend you see your gynecologist yearly to get check ups. better safe than sorry and there is no shame is asking for the tests.