I had severe nausea during my one and only pregnancy and yet have been told by medical staff that a second might be perfectly normal and vice-versa. I had a doctor tell me at the end that I might have had hyperemesis, but that she had just learned about it. Since I only had three weeks left, it was never officially diagnosed or anything, but I got some extra help anyway. From what I know, there really isn't an official way to "diagnose" hyperememsis. They will test your urine and there is some thought that it is related to levels of hCG (which I had a very high incidence of even in my second trimester).
Not all doctors and nurses know about it so ask about it at your next check-up. If you go more than 24 hours without food staying down (or, even more importantly, water). Go into an urgent care facility, get rehydrated and get help.
Now, in regard to helping with the sickness you are dealing with, HP or not, have a dry cracker or granola bar near your bed when you go to sleep at night. One good way to stave off actually getting sick (even if you feel really sick), is by always having a few bites and never letting yourself get truly hungry. Just a nibble or two before you actually get up out of bed, followed by a few sips of water can make a huge difference.
My OB recommended taking a daily vitamin (which I usually didn't keep down because it made me feel sick too), but again, I did find that taken with a bit of food, I was more likely to keep it down a little longer (if not, getting sick when there is food in there is a lot less unpleasant than when your stomach is empty).
Also, extra B12 helped a little, avoiding gassy foods and acidic foods helped ease the symptoms somewhat and listen to your cravings and aversions. You are pregnant so you don't have to politely eat that (fill in the blank here) that your friend made for dinner and brought over - even if you do need to politely say thanks and offer it to your husband to eat ;-/
Mention your concerns to your doctor and take heart! Even though I struggled for 8 of 9 months, lost over 5 lbs over the course of the whole pregnancy (instead of gaining), and had to have a drip to get hydrated a couple of times, my baby was above average in weight and length and perfectly healthy.