Is she pregnant??!!..............what are some signs?

her belly is really big and its not hay belly, she was wormed 1 1/2 weeks ago, her teets are big and full of a milky substance, she is lazy and doesnt like to be ridden, shes 20 yrs old and i just bought her About 2 weeks ago im not sure if she was with a stud or not but she looks about 6 or 7 months along. ill probably end up taking her to the vet but iwant to see if you guys can help answer this for me. if she is pregnant should i abort the baby, i wouldnt but shes old ad i dont want it to hurt her so should i?