Have you told your doctors you have discontinued with the medication??
It's one thing to discontinue and stay under observation in hospital and another to go home and stop the medication they assume you are taking. They only would have discharged you on the assumption that you are taking it, surely?
It's pretty dangerous to self diagnose - just because they don't know exactly what is wrong, it doesn't mean that erring on the side of caution and giving you these is a bad thing. Medicine is not an exact science unfortunately.
Blood clots can cause stroke/pulmonary embolism/death. They give you blood thinners to avoid the chance of a clot. SO if you are worried about a clot then take the thinners!! Sorry to be blunt but I think you should take the medication.
A c-section seems like a minor trade off for avoiding something far worse happening to you or your child.
No one on here should and can diagnose you.
Take the meds and get back to the GP/hospital to push for more tests, but take what they prescribe.
You can spend 6 weeks sitting down if you have to. Sorry but you can. Obviously no one wants to but if you are that ill that you can't walk around you need to acknowledge it and accept it and rest, whilst taking medication and seeking further tests. Believe me I know how horrid it is being ill when pregnant, I have had Pre eclampsia problems with all my pregnancies, but you just have to let it wash over you and adjust to it.
I hope it is nothing serious and works out for you