Depressed

Im 29 Weeks Pregnant ... So Today I Had My Doctors Appointment And I Was Told I Weight 184 I Started Out At 155 So I've Basically Gained 29 Pounds And I Don't Know How If I Eat Healthy And The Same As I Did Before I Was Pregnant. On Top Of That I Was Told I Had A Marginal/ low lying Placenta. Has Anyone delt with Any Of This Before?? Has anyone gained a lot while pregnant and went back to their pre pregnancy weight? Has any one had a low lying placenta and it went back to normal before birth? Please let me know!!!,