Well I can definitely give you an I've been there! I have a little one who is 3 now. I suffered from anxiety disorder throughout my entire pregnancy and still have episodes now and then. There was a time when my daughter was just a year old that I had to take her to a doc appt when she was sick with a cold. I was so anxious that I had a full on panic attack while in the waiting room sitting to be seen. When I have a panic attack I get D within minutes so I picked up the little one and ran for the bathroom. I am sitting there with my pants around my ankles and she is crying because she doesn't feel good, crawling on the floor, looking under fellow stalls, and saying in the LOUDEST VOICE EVER--"Mommy that poopy stinks!" I seriously wanted to die! I packed up the kid and drove home in tears without seeing the doctor--I felt like the worst mother that ever walked the earth. I mean if you asked me I would say that I would take a bullet for my daughter---just don't ask me to take her to the doc for a sick checkup, I guess. It was horrible, but you know what I survived. I went home, took a few deep breaths (and a couple immodium) and headed back to the doctor. I called my doc's office on the way and explained that I had gotten sick in the waiting area and had to run out--could they still fit us in please? I didn;t go into details and they didn't ask thank god! They accommodated us, checked out my daughter and we left with an rx for her in hand. Did that whole episode suck--well yeah it did! But you know what, I am here to tell the story-so it didn't kill me. If any thing it helped my anxiety a bit because it made me see that even if my biggest fears came true (having a massive panick attack and then the runs while in public with my daughter in tow and no hubby for support) it wasn't the end of my world. It was embarrassing, but not life altering.
I am telling you all this, so you can know you are not alone. Yes they have diaper stations in women's restrooms, but what are you supposed to do with the kid when you have to use the washroom? Here is my advice that may help you a bit with that. Never leave home without an emergency kit for the little guy--this should consist of entertaining books, some finger foods that don't spoil like cheerios and cookies, a juice box and sippy, clean blankets/wipes/diapers/clothes, hand sanitizer, and a memory chock-full of annoying songs for his entertainment. (think daddy daddy bo babby me mi mo maddy fanana nanna fo faddy daddy...now son who's name is next?) And above all else an umbrella stroller with a seat belt. If an attack hits and you need to run to the john-strap him in and use your bag of tricks to entertain him while you relieve yourself. You will probably feel silly singing and feeding him cookies, but it will keep him calm and people are very forgiving when you are dealing with a child, so you will probably even get a few sympathetic nods from fellow dads. And he can't get out of the seatbelt and touch a nasty urinal cake or something---small stroller is best because of the size of stalls. If you are worried about where you will be able to change him--that is what the blankets are for. Lay them on the seat of your car, park bench, second shelf in aisle two...you get the point. When they are in diapers you can change them anywhere.
Lastly, are you on meds for the anxiety? I was on Buspar ( a relatively low dose) for almost two years and it was a god-send. I didn't feel all drugged up or anything, it just took the edge off so I could relax a bit. I see you are on Lorazepam and personally I think that is not a good drug to rely on long term. It has side effects and it gives you such a euphoric feeling when taking it. The Buspar is more mild and just calms you a bit---but obviously talk with your doc before making any changes with your anxiety meds as some can be dangerous to stop cold turkey-you'll need to wean. And if you are really up for it, check out the book "The feeling good hand book". yes it is a bit cheesy, especially the title, but it has some great cognitive behavior therapy info in there for changing the way you think about things. That book along with meds and therapy have helped make it so I have barely any panic episodes anymore. I haven't been on meds in almost two years.
The book gave me some good ways to sort of talk myself off that ledge before it was too late when I was out. I have a great supportive husband, but its hard for him to understand fully when he hasn't experienced the same problems. I am sorry for the novel, I hope I have helped you at least a little. Feel free to send me a message if you want to talk more about this stuff.