Rashes on the bottom of my stomach?

Fungus? If you have belly flaps, this may be from a yeast infection which usually affects moist area of the body. If this is the case, try to keep the area dry. Use a anti-fungal cream if necessary. Without more details, any answer is a wild guess at best.
Doctor can evaluate. Rashes are hard to describe in words. Pimples, on a part of the body that doesn't normally get acne, may be caused by more dangerous bacteria such as staph. Scabies (a mite) can cause itchy rashes near the waistline. Insect bites occur there if a bug crawled along the waist. A doctor can evaluate and start treatment with antibiotic cream and/or oral antibiotics, if suspecting a bacterial cause.