Is It Safe To Take Arixtra And Coumadin For Long Time?

My husband, a very healthy 40 something, recently got lung blood clots on two separate occasions. Neither he, nor anyone in his family, has any prior history of blood problems. Tests ruled out common blood conditions such as HIT, Lupus, etc, leaving the doctors without an answer. Both times, he began with an H. Pylori infection, in late 2009 he was treated with Amoxycillen, and the subsequent lung problem was treated with a variety of drugs including Albuteral. Six weeks later he had a severe pulmonary embolism. The second time he got the lung clot in May 2011; he was given Sulfametazsol and Acetomenaphine for the initial stomach ailment, and was already taking a Heparin based drug due to the previous blood clot. We know he developed a blood clot within a month of the stomach problems, because Cat scans were completely clear of clotting a month earlier. The doctors want to put him on lifelong Arixtra and/or coumadin for life. I m terrified not only because of the side effects, but also because I know that these drugs, or interactions of drugs, w the H. Pylori caused the clots in the first place. HELP!