What to expect after a ectopic pregnacy?

Three weeks ago i went to the ER for pain in my stomach and bleeding. My period has been on two weeks prior.The doctors took a blood and a urine test with came back positive. Finding out i was pregnant was overwhelming for me, because of the pain and the the bleeding they proceed to give me a sonogram. The doctors first said the found a 7 cm cyst in my ovarian. They ask me if it was an unwanted pregnancy i said yes because i thought i was gonna have alot of complication with the cyst being there. The moment later they said it was a ectopic pregnancy so the gave me a shot of methotreaxate. My hcg level was 982 on that day. After bleeding for 20 days three weeks later my hcg level slightly went down to 852.I took a second sonogram and they said there nothing there. How long does it take for my level to go all the way down? Being as tho my hcg level is 852 why is the nothing there in the sonogram? Will i be able to get pregnant again?