Yes! I went (am going through) the same thing with my second son, who is now 17 months. He is extremely picky with food (eats like 10 things, no matter how often and hard I try) and would only drink a few ounces of milk/water a day. His morning diaper would be fairly wet, but the rest of his diapers were barely, barely wet. It was totally stressing me out. I tried everything-- whole milk, 2%, 1%, soy milk, rice milk, watered down juice, pedialyte, pediasure, flavored waters, homemade juice popcicles, etc. AND I have tried all sippy cups, regular cups, straws, etc. I have been as consistent as possible, and would try to be patient and calm, but it was hard and stressful. He just wouldn't drink! It was so weird, because my 1st son ate everything-- a healthy and varied diet, and drank tons and had very wet diapers at every changing. Anyways, after about 4 months of trying everything I could think of, he is finally up to maybe 10-12 ounces of milk/water a day. Still nowhere he "should" be, but compared to where he was a few months ago, it's a lot!
My only advice is to hang in there and keep doing
what you're doing and don't give up. Keep checking in with your pediatrician, too. Good luck!