It is definitely possible to be re-traumatized in therapy if the therapist is not skilled in dealing with trauma issues. My therapist was rather adamant about what should and should not be done in relation to exploring past trauma so that a client does not suffer re-traumatization.

Is your therapist skilled in handling these flooding memories? If not, perhaps you may need to seek out a therapist with different experience. Telling you to "forget" the memories and "try positive thinking techniques" doesn't sound like much of a plan. It sounds like avoidance.