Could a serotonin or dopamine deficiency in one's blood cause depression/anxiety? or are the blood ser. and dop. unrelated to the ones in brain?

Unrelated: Assays for serotonin and Dopamine in the blood are not reliable indicators of these substances in the brain's synaptic spaces. You may be offered these assays by "independent medical thinkers", but you would not do well to rely on them. Depression and anxiety are biopsychosocial phenomena and must be addressed as more than "chemical imbalances" -- their many aspects are all important.

See a psychiatrist: With symptoms of insomnia, hopelessness, and a high sex drive, i would wonder whether or not you are bipolar and in a mixed mood state. A psychiatrist will have to determine this. Blood levels of neurotransmitters do not correlate with levels of neurotransmitters within the mood regulating limbic system portion of the brain. Therefore we have no blood tests to determine what type of mood a person is in. In fact, when it comes to bipolar disorder and especially mixed mood states the underlying pathophysiology remains unclear. Please see a psychiatrist or a physician competent to handle your condition and best wishes to you.

Weakly related.: The serotonin and Dopamine in the blood regulate different processes than the ones in the brain. In fact, IV Dopamine is what we give to people with heart failure to make heart pump stronger.