ttc for 3.5 years, already have a 4 year old

Hi ladies this is the first time iv posted on here but AF has just arrived so I thought hey why not! So We have a daughter who turned 4 in Feb and have been trying for another baby since she was born (never used any precautions) but have been properly trying for about 3 years. My cycle is quite regular maybe 2 days give or take but wasn't any different when I got pregnant with my daughter. We have just decided that it's time to see a doctor but I'm scared and nervous as to what happens next and I was just curious to see if anyone else has been in a similar situation and had a happy ending. I know some people would die to have the child I already have and I am so so grateful I already have had a baby but I can't help but be disappointed every month when hope of a little brother or sister is out the window x thankyou