1998 Dodge Neon Oil Leak

Hi, I have a 1998 neon. When I got it it had a small oil leak. It just dripped here and there, would be fine between oil changes for about 4,000 miles. About 4 months back the water pump froze on me, causing the timing belt to go and 2 velvs. I had those replaced. They also replaced an oil sensor they said was causing my leak. I havent noticed no drips on the ground and I have been keeping a close eye on it. The underbody was always a little more oily than it should be. I have noticed that im running out of oil now. I havent seen any leakage, but have to fill it up about once a month now. The oil light doesnt even come on to show me that im low. I noticed when I changed my starter that I was almsot completely out of oil, but no oil light nor did it even show a sign of overheating. Could you guys throw me some ideas of what else could be causing this problem plz. Thx