lump on lower belly of dog

my dog is 10 years old and is the average sized pitbull. a little bit of a month ago, i noticed she had a lump underneath her “mutated” nipple that shes has ever since she was a puppy. when we took her for her shots when we first got her, the vets did not seem concerned about the nipple. her mutated nipple has gotten redder and more swollen-looking from the lump. this lump is warm to the touch, and there is redness and red spotting on it. though when i touch it or gently press on it to feel the size, she does not flinch or whimper, and lets me feel it without a problem. i dont think its painful for her. it started out small with no hotness or redness, and then gradually got bigger and hotter. it has not grown in size for a little bit though. she is spayed and has been for about 4 years now. she has been eating fine and pooping fine, and has not been acting ill. she acts like her crazy self so at least thats comforting lol. for the past couple days she has been eating grass and throwing up, but afterwards she eats her food and poops later and doesnt throw up, so i dont know if the two are related. i dont have money to take her to the vet right now, but i am currently saving up as this is a huge concern for me. does this look familiar to anyone else? has anyone else’s dog had this happen to them? if so, what was it and how did they treat it? 

Hello!  This nipple could have suffered physical trauma (especially since it was large and prone to scraping anyway); it could have become infected; it could have become cancerous; it could reflect mastitis or even a wider systemic infection.  I'm not sure whether its related to the vomiting but it could be and  either way, that could be urgent and should be triaged.  This is where the vet tries to get a good picture of what's going on and  classifies it as an emergency, one to see relatively soon or one to see when it's convenient, financially sensible etc. Triage would be the first step.