What Does The Absence Of Gestational Sac Indicate?

hi, mine LMP was irregular its of 40 days and started on 24 feb ,on april 3 i did hpt it was faint on 10 april i did hpt it was dark positive.the hcg was 514 but no gestational sac .on 15 april hcg was 3800 but stil no gestational sac.i want to ask .is it normal . i have no cramps ,no spotting