Bathroom phobias are normal at this age. The thought of having to remember to use TP, flush, wash his hands and dry them is probably a little overwhelming.
Claiming inadequacy is also an attention getting technique that children with delays tend to keep using because it works. So from now on don't remind him to go, and if he goes in his pants, well, that's his problem. Cleaning him up should be an emotionless get it over with effort in order to keep him from feeding off the negative attention he could be craving. This site talks about all of that: http://lifematters.com/step.asp
As far as the social skills go for right now, I would ask the teacher to just let him off of the expectation of being paired with another kid. Some kids just aren't social when they're working so hard to cover other deficits. His speech delay may prevent him from interacting or he could be being paired with some one where he can't get a word in edgewise.
Also make sure you're reading to him for 20 minutes every day alone. If you want to check out books on using the potty or making friends and read only them each time then do that. Try to avoid talking about "problems" with him and focus on talking about good things with him. Praise him a lot, "Insert name in here, YOU did a great job putting that toy away"... or what ever he did besure to say his name, you and exactly what he did. This will boost his self confidence and show that you really are paying attention to him rather than issuing a "good job" just to get him to leave you alone.
So if he has a younger sibling you start a bath time routine where he gets to play on the computer at preschool.com, pbskids.org, or starfall.com while you're bathing, reading and putting the other child to bed. Then it's his turn.
If he's the youngest you start with him a half an hour before bed time he has a five minute bath, five minutes to brush teeth and get dressed then 20 minutes of you reading to him before he goes to bed. Dad should do this when he gets back from deployment. Then you start the next oldest child's routine after he's in bed. the older he gets the more you can transition this to him reading to you, covering homework problems or talking.
I know it's hard to do this alone but there is support out there for you. Family and Children's Services can help with the social skills.