Blossom, you came on here asking for help. Since no one on earth can give you a diagnosis over the internet whether your mare is indeed preggo, if she's just fat, if she's ate up with worms, if she has a belly full of pus due to being turned out with a potentially scummy stallion, or if she might be suffering from a massive tumor in her gut or anything else along those lines, calling a vet is the most reasonable response you are going to get. There is no way for us to know, especially based on a few poor quality pictures posted over the internet. The only person getting snarky over this is you. Telling you the wise choice is to call a vet is not a offensive statement meant to upset you, it's simply the most logical answer to the question you posed. No reason for you to get nasty to those you asked for help from, however guilty your conscience may be.