Is going to therapy or taking antidepressants a lack of faith

No. Using medicine and wise counsel is biblical, not carnal. Scripture treats physicians as a normal good - Jesus said 'They that be whole need not a physician; but they that are sick' (Matthew 9:12), Luke the Gospel writer was himself 'the beloved physician' (Colossians 4:14), Paul prescribed a medicinal remedy to Timothy (1 Timothy 5:23), and a 'merry heart doeth good like a medicine' (Proverbs 17:22) assumes medicine does good.

Depression and anxiety involve the body - brain, hormones, sleep, trauma - and treating the body honors the God who made it (1 Corinthians 6:19-20); we do not accuse diabetics of faithlessness for taking insulin. Counsel, too, is repeatedly commanded: 'in the multitude of counsellors there is safety' (Proverbs 11:14). Prayer and treatment are not rivals - pray AND go; God regularly heals through means.

If a voice (inside or in your church) says real Christians should not need help, test it against Scripture's kindness: 'He shall gather the lambs with his arm, and carry them in his bosom' (Isaiah 40:11). Getting help is not weak faith. It is often faith in action.