Pregnant Again ? So Fast.

Hi So My Boyfriend And I Have A 3 Month Old Daughter We Had In August & Were Both 20 & Shes Both Our First Child. I Haven't Got My Period For November, I'm 3 Days Late & It Doesn't Seem To Be Coming Any Time Soon. I'm Not Having Any Spotting Or Cramps. My Question

Is Should I Be Seen or Wait ?

What's The Max Amount Of Days To Miss Before Worrying ?

We're Not In A Good Situation For Another Child. Both Still Young , What To Do If I Am Pregnant Again So Soon ?