Ignition switch fuse keeps blowing

I had my starter replaced thinking my starter went out. Ended up having to buy a new battery. Before battery replacement, the fuse for the ignition switch had blown out. Replaced it several times only to have it blow out again and again. I cannot get my van to start. Both the old and new starter work perfectly fine when hooked up to the battery. But no matter how many times I've bought and replaced the ignition switch fuse it blows, even without the key being in the ignition. How can I find and fix this problem asap?