What you have described is sexual dysfunction, unbearable anxiety, and significant fear of abandonment. These in combiation are almost always caused by trauma.
The description of your shame and guilt over your nudity, and sex may be caused by messages given by your family of origin. These messages must have been very harsh and probably were reinforced by physical abuse. Or, they may be the result of sexual abuse. It can take a long time to remember the events.
My daughter had her repressed memories return after 25 years. I would definately agree with your girlfriends that some abuse or trauma lie behind these behaviors. The idea that promiscuous sex (one night stands with multiple partners) and revulsion and guilt about being touched and avoidance of being nutured, or physically close all point to trauma.
Whether that trauma was sexual abuse, abandonment and neglect, or emotional abuse reinforced with physical abuse, I wouldn't know any more than you. However, exploring that possibility certainly seems worthwhile.
There is support and resources here for that exploration. You know for yourself that these experiences are not self beneficial. Panic attacks never are. As pero indicated internal conflicts can be overwhelming. Giving yourself time to explore is necessary. These are not issues to be overcome quickly. Eventually, a trip down memory lane, may not be comfortable, but is essential.
Welcome to the journey and may you find comfort peace and resolution to these conflicts.