A.C.
Look into respite care, so you can have some help with your son, especially now when you're expecting another little one. I do not know if they come to the house, but I do know (at least in Madison, WI) that you can take a child there when you need a little breathing space. You might have something in town you can tap into, since your child has special needs. I didn't find many resources where I live for my child, though, and I live in a university town (where you'd think there would be a lot of resources. But only for those kids who are "diagnosed." My daughter doesn't have a "diagnosis" or a code; her Childhood Specialist only confirmed she has SPD, but she doesn't have an official status in her file).
Does your healthcare pay for a Childhood Specialist you could take your son to, someone he can talk to who can "work out" with him how to handle changes and get him "on track," so he's not continuously fighting you?
My daughter has Sensory Processing Disorder, so I feel your pain. She went and saw a Childhood Specialist from age 5 to 11; right now, we've switched healthcare insurers, and I haven't bothered getting anyone new in our new provider. However, she has learned to handle herself and situations so well that I'm not sure I will. But we have a referral option open in case it's needed (the teenage years are coming, after all). My daughter also has anxiety and OCD along with her SPD.
Basically, it comes down to "retraining" children in how to handle situations, since they lack the knowledge. Your son also could have some sensory issues when it comes to showers/water/etc. My daughter had issues with taking baths starting at age 2 that lasted until she was 4 or 5. I had to take baths with her and "play" for awhile in the tub. She eventually grew out of that and now takes showers. We never did figure out what part of taking a bath she didn't like, but apparently, it's a very common problem among kids with sensory issues.
You state your son has issues with bed wetting; does he also have problems with constipation or streaking in his underwear? If he's constipated and not eliminating as needed, the feces will push on the bladder and cause him to have an overactive bladder/accidents. That would be something I would think about and look into. If he is constipated and you take care of that issue, you might also be able to get rid of (some) of the bed wetting. Someone stated there is also a device that can be put inside of the underwear for boys that, at the slightest drop of moisture, will "alert" the boy that he needs to go. If your son is a deep sleeper, though, that might not work.
I understand about the 5:30 am wake up. My daughter also gets up that early. She doesn't need/doesn't take a shower in the mornings, but needs time to get ready. She gets on the bus at 6:45 am.
You're going to need to enlist your husband/significant other to help you a lot more than what you're currently getting. What are you going to do once another baby is in the house? Is your son acting up more lately, knowing that there will be another person to whom you'll need to dedicate your time? Has your son acted up worse since the 2 year old came on the scene? Kids with SPD and Aspenberger's, Autism, etc., have a hard time with change and/or sharing mom, dad, other trusted adults with other children. If he's acting up this much with the new baby coming--who isn't even here yet--I can only forsee him becoming even worse after the baby's here and your attention is devoted to him/her.
I would definitely advocate that your son start seeing a Childhood Specialist. It will greatly help him with learning coping mechanisms, and it will help you, having someone to talk to and get some ideas on how to help your son.
It's a long, tough road. But it can be transversed. My hat is always off to those who have more children than just the one with special needs. My husband and I knew our daughter was special when she was two years old. We made the conscious decision that we weren't able to deal with her and any other children at the same time, so we decided she would be an only child. That has worked for us. It's saved us stress, and it's allowed us to take the time our daughter needs to work through her issues and give her/teach her coping mechanisms.
If you have more questions, please don't hesitate to contact me.