Need some advice

Just wanted some input on people's feelings I was with this guy for four years and he wanted kids but I didn't want any with him I didn't tell him that of cours but we tried and couldn't conceive we broke up and now I'm with my husband and I really wants kids but I just have it stuck in my head that I can't have any because of pervious relationship how do I start thinking more positive about conceiving a child instead of always thinking it won't happen im only 24 so I know I'm at a good age to have children I just can't stop thinking negative because I really want a child I just think I think this way so I won't get my hopes up