First time sex

So I lost my virginity about five months ago and all in all I’ve only have had sex about 5 times and it wasn’t consecutive either. My bf and I want to begin having sex but just him fingering me with four fingers hurts like crazy and slightly burns. But the burning sensation goes away within a few minutes. I know it’s not some STD or anything because I haven’t even done it with that many people or that many times. Is it just because I’m really tight and am not used to it? Is it normal for it to be so painful for a bit? Also any tips?