My tropical fish are dying when i added a new pregnant fish..HELP!?

A couple of days ago,I just added a pregnant guppy to my 10 gallon tank,with a male.i have a dwarf gouriami {not sure how spelled} an angelfish,candy cane tetra,pleco,betta and a blue lobster. A day later the male guppy went missing in the tank,I though he could of been eaten, but there was no blood,guts or bones in the tank! The female is fine. Then a day later my angelfish died. everyone lived in harmony,until i added a PREGNANT fish. I might be over crowding the tank,but i noticed my dwarf gouriami seemed to be chasing the other fish away when they came near the pregnant female. If my tank is over crowded,, what do I do? Do I have to take the fish out? Is my water Bad? didnt think so because i checked all of my fish,,no white spots or any diseases} The dwarf gouraimi chases the fish,usually,now that some died,,i only have 5 fish. The water is crystal clear,,some bacteria,,(which they need) i had these fish for 5 months,,nothing happened like this before,,HELP!