Toddler Sleep deprivation?

My 15 month has been sleeping horrible for a one whole month. I’m honestly about to have a mental break down. Because I don’t know what to do. He gets up from 1-4am every night. Then falls asleep for a hour and back up. He is so overly tired he is fussing all day long. Because he’s only getting 5 hours of sleep at night. Naps are just as bad. Falls asleep for 30-40 mins then back up. He still is extremely tired and I try again for another nap and refuses it even though he’s so tired he’s falling down and whining all afternoon. His normal bed time was 7pm but he can’t even make it lately because of how tired he is. He has been going to bed at 6pm. I’ve started to become angry and frustrated with him because we’re beyond tired. I don’t know what to do anymore. Ive called the doctor to see if they can suggest something. Before he was going to bed at 7pm waking once at night for 1 bottle and staying asleep until 8am. I’m so clueless and feel like crying all day long because I’m frustrated with my son and not sleeping. Also because I feel for him on how tired he is. Please help any suggestions. I can’t ask my husband to watch him because he works nights and he’s also only getting 3 hours of sleep because when he gets home my son wakes up to start his day at 5 am and I’m leaving to work at 5am... really struggling here