Trying to conceive

Me and my other half have been trying for 2 and 1/2 years I am devastated every month when I get my period... I have a 3and 1/2 year old and she keeps me going I feel selfish because I was lucky enough to have my daughter but I have always wanted a lot of kids and now Since I had a miscarriage back in September it's only made it harder....how long have you been trying and what keeps u from giving up