Antibiotics for two weeks before FET

Of all the medications for my upcoming FET (April 5th), I am the most worried about the antibiotics. I have to take Doxycycline and Flagyl (Metronidazole) twice a day for 14 days. I've taken Doxy before no problem. I took Flagyl for a week after salpingectomy and it was HORRIBLE. Severe constipation, nausea, lost appetite, malaise, etc. I took them with food and ate yogurt every day and still awful.