I hope you are well today and thank you for your question.
It doesn’t seem the theme issue but your site specific so please troubleshoot it to find the bottleneck of the issue.
If you can’t find it then you can consider hiring a developer to find it out for you. You can hire a developer from any freelance site. Shufflehound recommends the developer https://www.upwork.com/freelancers/~011652ffec8865c6d5