I think your question title about how to “fully be a Christian” is different to what you are asking (about not feeling alone etc.). I would not equate the two since I think you can fully be a Christian once you have repented from sin and believed in Jesus (some churches would like you to be baptized to formalize this or do other things but I think the bible teaches that basic belief is enough).
Changing your feelings or life situation is a different matter. You could try some Christian counseling to see if there is anything different you could be doing, or whether a specific church group / social group would help.
Being a young mother with 4 children will also mean you are busy and might need some time out to reflect or “feel” anything. It can also be hard when people “gush” about a “relationship with God”. I’d also recommend not worrying too much about what they might or might not be experiencing. Maybe they can come and help with the kids one day!
Published 17th November 2019