Needing Advice (FTM)

Hi everybody!  I know this might be a sensitive topic to some but I am a first time mom here and a little nervous!  For a while I've had constipation about 2-3 times a work and the other days I am fine.  Today while using the restroom I saw I was bleeding.  I'm about 18 weeks so the miscarriage instantly popped in my head.  But then as I was wiping I noticed something stang and blood was coming through there.  I got scared but figured it could only be a hemorrhoids.  I'm nervous about this, so o guess I'm asking Is this normal?  Or should I contact my OB immediately and take a trip to the E.R.?  Advice please!