So anxious driving, I have to pull over and call for help!

You seem to have developed a driving phobia, but it could also be a more general anxiety disorder, or more specifically agoraphobia, which would be feeling anxious anytime you leave your house, either by yourself or with someone else.  It is also likely you are having a panic attack, by the time you have to pull over and call your husband for help.  I will start with a few questions for you:

Are you anxious only when you are driving?  Or are you anxious when you have to go somewhere by yourself?  Would you get anxious taking public transportation (if it exists)?  Are you anxious walking somewhere?

If only driving makes you anxious, does that only happen when you are alone?  Do you get as anxious with your husband sitting next to you in the passenger seat?  Does that feel safer?  Or would you feel even more anxious with a passenger in the car?

If you sit in the car long enough by the side of the road, are you able to calm down eventually?  Or do you stay just as anxious and panicky until you call your husband?  Do you start to feel better as soon as you know he is coming to get you?  Or do you remain that anxious at least until he arrives?  How long after that do you still feel anxious?  When do you eventually calm down?

If it only happens when you are driving, with or without someone else along, then there must be something specific about driving that makes you anxious.  You say that you are not able to come up with any reason for it.  I would suggest noticing what your thoughts are as this develops.  Have a notebook handy next to you.  When you notice thoughts that you have as the anxiety develops, write them down, when it is safe to pull over to the side and do so.  Especially record what you are thinking when it becomes too much for you, and you have to call your husband.  Do this when driving by yourself, as well as with someone else along.  If you do this a number of times, and on several occasions, you may notice that certain thoughts recur frequently, if not every time.  Once you have an idea about your usual sequence of thoughts, you will be able to challenge each one of them individually.  The goal is to notice your negative (and fearful) self-talk, and to replace those thoughts with statements that are more true, positive, or at least more balanced.  You may not be able to do this at the time you first write them down.  But look them over when you are calmer and in a less stressful situation.  You may need the help of another person, such as a therapist, or perhaps a family member or close friend.  Once you have identified replacement thoughts, you will likely be able to remember them and use them, while they are occurring, in the process of becoming anxious.  You will get better at this, with repetition over time.

As for panicking, notice the physical symptoms you experience when it gets to that level, such as racing heart rate, shortness of breath, sweating, dizziness, becoming disoriented.  Each time you become aware of such symptoms, say to yourself, "I recognize what's happening.  I am having a panic attack.  I have experienced and survived these before.  It will take some time for this to subside, and I need to wait it out, until I calm down, and come back to normal."  This can take a minimum of 10-15 minutes, and possibly longer.  Remember to breathe, and focus on that if you can.  It has been said that panic attacks are getting very anxious about being very anxious.  The more you recognize the process, especially that escalating second layer of anxiety, and give it time to resolve itself, the less time it may eventually take.  Try to do this when you have to pull over, and give it the time it needs, *before* you call your husband.  As you get more used to and more comfortable with that, you may find that you have to call him less often, and can proceed by yourself eventually.  It is still very inconvenient, and probably scary.  But the more you can manage the situation, the better you will feel.

You may benefit from working with a therapist on this, especially if it may relate to something that happened in the past, or something else currently going on in your life.  Be sure to choose one who understands cognitive behavior therapy.  Fortunately, most experienced therapists do use that method, among others.  Best wishes for learning how to cope with and manage these episodes!