I and my husband are married since 5 years We

Patient: I and my husband are married since 5 years. We are planning for baby from last 1 year. Although we never used any protection before but we were also not serious about getting a baby. 4 months back while we were visiting gynec, my husband semen test was found some issues. His sperm count is 8 million and motility is about 10%. He has been taking medicines from diff doctors since then but we are not seeing any improvement. there was only one test 3 months back when his count came 20 million , otherwise it is always showing 8 milions only. My doctor got some tests for me including hormone tests, everything came normal. Doctor is advising us to go for IVF. is it right decision to go for that? We are scared. Can there be some issue with my fallopian tubes . Can getting them tested help us? Per theory only one sperm is require for pregnancy , then why 8 million sperms with 10% motility can help?