Stressed after maternity leave

I returned to work three weeks ago after having Ordinary Maternity Leave of 26 weeks. I was anxious about going back anyway, just with leaving the baby etc, but I've had nothing but stress since I returned and it's really starting to get to me now.

My employers were useless even before I went off on maternity leave. I was having to chase them constantly to get them to fulfill things they were supposed to be doing and I ended up breaking down in work just from the stress of it all. I thought things would improve when I went back, but it's worse. Firstly, they placed my maternity cover in a role that I don't and have never done. I met with my manager back in December and was promised that I would be given my orginal role back and not to worry. I returned to work and got to see my manager for 5 minutes - where he informed me that I would be going to the new role. I refused to do it. I was then left for the rest of that week literally doing nothing. The manager was unavailable to talk to and did not respond to emails. 

At the start of my second week back, I was given another 5 minute meeting with the manager and told that I wouldn't have to do this new role that I could take over from someone else doing my original role, who had agreed to transfer. I was told to wait until they had discussed it further with this member of staff before doing anything. The week passed with me doing nothing again and no info from manager. At the end of the week, with me chasing him up, he finally said oh yes I did speak to them, just go and sort it out. Before I went off on maternity leave, I was transferred into this role and only did it for a couple of months. It is vastly different to what I had been doing prior to that so I really don't know what it is I'm supposed to be doing anyway and after being away for 7 months really need updating on the service!

This week, the member of staff I am supposed to take over from was off on training. So for the past two days again, I have been left literally doing nothing. An email to my manager got the response that I should just head up to the main offices in another part of the city and link in with one of the teams there. I have no idea what teams he means, who they are, where they are based!! How can I do that!!! He seems completely oblivious and as he is also my supervisor, it's not as if I can even ask anyone else for a bit of input. There are also logistics of my role that he hasn't even considered - for example he's asking me to just to sort out and take over my colleagues role, but she works full time and I'm now 4 days so am I being expected to cover her entire workload in less days? 

I've been getting more and more anxious about this as the days have gone on but have been forcing myself to get in and just deal with the sickness and shaking. Today though I just haven't been able to face it and have called in sick after spending the morning heaving and shaking. It's really affecting the time I'm spending with my baby now because the anxiety is there all the time and I keep bursting into tears and am always worrying. Am I wrong to think that I should be getting more support than this from my employers??