Sauna?

I'm 18 weeks pregnant, but I currently have a stinking cold, I'm so congested and I can't do anything about it apart from steam inhalation, which gets me onto the sauna? Tomorrow I have a mum to be spa package booked, I don't wish to spend this day sniffling and sneezing and was wondering if a 3-5 min sit down in the sauna followed by plenty of fluids be all that harmful? It would just be to help shift some congestion before my treatments? The spa I'm going to are even changing the temperature of their hydro pool so it's safe! I'm very excited just very bunged up and sniffly!