Pain during sex

I've been with my boyfriend 5 months now, and in the last month I've had excruciating pain while he's putting it in.... And afterwards I can't walk properly nor sit down.... I went to the sexual health clinic when it first started and I'm clear of all STI's and I had the implant fitted, they treated me for thrush and it worked for a few weeks but it's come back again, it's not itchy or anything like thrush is... It's just painful!!! Help!!!!!