Have you thought of leaving something personal that your son is familiar with when dropping him off, this is a link with you and home and may re-assure your DS that you are returning for him, but dont make it a cuddly that your son will latch onto and want to carry around all day, just something youve forgotten, scarf, glove etc. Childminders cannot ensure a child will be settled before the parent returns to work, it sounds as if your settling in period was far to short, was this your choice?? did your C/M not advise you that it could take time, I totally agree with Ripeberry it can take upto 4 weeks to settle in, it depends on the individual child, each child is unique and reacts to change in different ways, thats what makes him an individual, and dont worry if he displays any regression in his development, this is to be expected, (he may go back to thumb sucking, become clingy etc but if you work with your C/M he will soon get over it).
I always encourage parents to work with me for at least 4 weeks to settle their child in prior to starting full time and they returning to work, it gives us chance to get to know each other and build up a working relationship, we are after all sharing the care of your child, and we will, like you, want what is best for him/her. I also, always encourage parents to discuss their concerns, worries with me, if I dont know I cant help. Have you discussed your worries and concerns with your C/M?.
Give your son time to settle, trust your childminder and work with her to see him and you through this emotional period. You sound very caring and a lovely mum, I'm assuming you are a first time parent and maybe deep down you are feeling a little guilty at leaving your son, but you dont have to be, it is difficult to leave your child with some-one else but your C/M is there to support you through, just hang in there once he gets used to the routine, you will be amazed how confident he has become and how relaxed you will be, you may even choose to work more hours.