Think calm and peace Kara. I know it is difficult, but please try not to stress.
I think Stormy is progressing just fine. If she takes a little longer to cook this baby than you think she should, then that too is fine. So many of the mares seem to be going well over their due dates this year, and as you said Stormy ran with the stallion and you simply presumed that he caught her at the first date, because you didn't see her covered again??
Others will probably scream at me, but FORGET about milk testing - apart from the fact that (given the possible second covering date) you are too early to think about testing, it also bothers her and stresses you because every time you read the results you are worrying because there is no change! If you really want to test, then wait until she has formed a bag that shows she has plenty of milk in it and not now while she is filling the milk glands in the front.
Neither would I think about trailering her to a vet, far too stressful for her and anyway the latest that mares should travel before foaling is 4 weeks, preferably before this. We moved our mares from here to Cathy's farm this year 5 weeks before they were due (and we had the correct dates as they were hand bred just the one session). One mare foaled 2 days later, luckily the foal was ok, but was weak. A second mare foaled two days after this out in the field, no dropped tummy and no milk to speak of, we lost the foal as it never got out of the bag (the mare was happily grazing in the field 2 hours before). The third mare did manage to complete her pregnancy and foaled with all the correct signs and safely in her stable with Cathy assisting. Did we have the problem with the first two mares because we travelled them? We will never know, but we will not be travelling them in the future unless it is months before they are due!!
So please try to relax and trust Stormy a little. She knows what she is doing and if you step back and leave her be, then perhaps you can both enjoy these last weeks of her pregnancy together. She is not ill, she is showing no signs of ailments etc. She may be unomfortable on occasion when the foal is lying in a different position, but this is normal, just as it is normal for you not to be feeling or seeing much movement from the foal - it will often depend upon how much space there is in her tummy because like us humans, some carry more 'water' round their babies than others, which, of course cuts down on the space for movement. Spend time with her, just observing her, getting to know how she feels as she progresses, watching her changing shape and understanding her different moods. Be ready for the possible day that she seems to really want your company - it might mean a foal that coming night if all else looks right (it has happened to me with several of my girls).
Good luck - you will both be just fine.
