It is reasonable and healthy for all of us to have a dream which surprises us or shocks us occasionally. As dreams partly deal with aspects of our urges and fantasies which we do not allow in waking life, such occasional dreams are safety valves. It is healthy to be able to allow a wide range of dream experience, from the holy to the deeply sexual; from outright aggression to tender love. In fact we gain an idea of the depth and broadness of our own soul—whether or not our psyche is narrow—from the range of dreams we experience.
If obscene dreams assail and worry us again and again, however, then there is a problem in the way we are relating to ourself and the exterior world. Psychotherapeutic counselling might help.
The dream symbol you are looking for is absolutely there, try searching the symbol one by one.