Look sister! Have is used in both ways; as a helping verb and as a main verb. WAS HAVING has have as main verb whereas HAD is a helping verb. Another difference is of tenses. WAS HAVING represents past continuous and HAD past perfect. Hope this helps you.

Had is the past of have. Was having is the past of am/is having. I hope that someone can explain it better than me :) Kisses!

They're both actions that take place in the past but: had (past simple): "I had lunch". It's something you did in the past and which is now over. was having (past continuous): "I was having lunch". Still something you did in the past, but this time you wish to put the stress on the action itself, on the thing you were doing. So you can say for instance "I was having lunch while the phone rang", but you cannot say "I had lunch when the phone rang", if you wish to say that the phone actually interrupted your action.