Separation anxiety.

Dear Dr. Marie, My family and I adopted Champ, who is a 2 1/2 year old pit-bull/terrier mix four months ago in July. He was a stray on death row in a shelter who was founding roaming the streets alone dragging a chain around his neck. Someone from the shelter brought him to a local rescue group/foster home in which we adopted him. We don't know much about his background except when he was in his foster home he was great with other dogs, cats and children. (We also have another dog, Brownie, who is a ten year old beagle and four cats.)Champ is a great dog; he is smart, playful, gentle, and absolutely loves people and our other dog and cats.Champ is extremely attached to me and my children (two girls ages 13 and 9).I am a stay-at-home mom so I am home with him, take him for walks, etc. My children are huge animal lovers (like me) and love Champ. Champ follows me around constantly, if I sit down he sits right on top of me and often does the same to my husband and children. It is almost impossible to get out of the house because he goes crazy trying to get out to go with me or my family.I take him with me whenever possible but obviously he can't go everywhere. He is also very anxious. If my children and husband and I are even laughing loudly Champ will shake uncontrollably. Even if someone is even talking loudly Champ will sometimes sit and cower and shake horribly. I know Champ's life before we adopted him probably wasn't the best. I don't know if he was left outside, abused, etc and I am sure that is all playing a major role with his behavior. I also know that dogs are pack animals and don't understand why they can't be we us all the time. We always give Champ lots of love and attention and I take him for two walks a day. I have also tried to desensitize him (pick up my keys and not leave, put on my shoes and not leave, etc). But he is making very little progress. I don't know if I should pursue this further as far as him needing medication or what else I can do. I don't want to put him on medicine unless it is necessary. We love him very much and I want the rest of his life to be happy. I hate to see him upset or suffer especially when he shakes when nothing is even wrong or get so upset when we leave the house. I also have been leaving the house for a minute and coming back so he knows that I will be back! I was going to bring him to our vet but I wanted to start with you first and see what you suggest. What do you think and suggest? Thank you for your time and help. Have a good day. Sincerely, Lisa and Champ