Not been here for a long while but wanted to reply to this question as it is of interest to me as it something that I had last year. I had multiple blood clots in my lungs and also a dvt in my leg at the same time. I was very seriously ill at the time. In the past I have had heart attacks and then had open heart surgery so I was at a greater risk of something like this happening. Happened a long while afterward but still a shock though I can tell you !!
Just some information from a patient point of view not a medical doctor one. Multiple clots or even one can and do start from a your leg caused by a DVT, not in all cases of course but in many many. The clots can be large or small.
The lungs contain blood vessels, which are derived from the pulmonary arteries. The pulmonary arteries break up into progressively smaller and smaller branches until they form small capillaries. PE's start off as clots that may come from your leg, pelvic, or abdominal veins, or even occasionally in the right side of the heart. These clots then travel through the bloodstream to lodge (embolise) in the lung arteries, cutting off further blood flow through that artery. This means that the region of lung normally supplied by this artery is no long able to function, as inspired air does not come into contact with the circulation.
One thing in your post was strange to me in that you said the clot you had won't go away, it will be there for about 6 months. This is very weird because the first thing that is given to you when a clot like this is discovered is that you are given a strict course of blood thinning injections into your tummy to disperse the clot. Check this with your doctor for me will you ?
Clexane/enoxaparin, which is a type of medicine called a low molecular weight heparin is the one normally use to stop blood clots forming within the blood vessels. In a lot of cases, Coumadin/Warfarin is given and you may be on it for life. I am.
I have APS though and have had blood clotting problems before, but never as severe as they were last year. Because of my APS, my INR levels have to be higher than the 'norm' and unfortunately mine fluctuates so much that I have weekly visits to the GP to keep a check on it. Pain to do but the safest thing to do also.
Thing is you don't have to have lupus as you know to have pe's and because you have lupus it doesn't mean you will automatically have them.
Hope this makes sense. I have been having a lot of problems lately and my head is not working properly. Hope this is of help to you. Take care.