could I be pregnant? advise

Ch
I need some honest opinions and a bit of guidance for the future. 
 
I have taken 9 pregnancy tests at home with first response, some with morning urine and some in the afternoon. 
1 done at the doctors  but I think I would have been too early for those results like only just 3-4 weeks after I had sex and they were urine pregnancy test.
I havnt had sex since March... That was 16 weeks ago. 
Is there any reason if I was pregnant that it wouldn't show up on a pregnancy test? They have all appeared to be negative. 
Doesn't your hcg double each day? So if I was to be pregnant would one of the test have shown a positive the further along I got? 
Sounds like such a dumb question, it was my first time having sex with my long term partner and I have still be getting my periods but they have been a bit weird. Some go for 4 days and some go for 3 but still the same amount of bleeding and I have been getting spotting a few days before my period week on the pill. I have still had cramps as well. 
I have had like a funny feeling in my lower stomach and it feels like pressure when I push on it. I have also had heart burn and tingly boobs throughout the whole month that then get sore to touch around two weeks before my period , when I get my period my boobs stop hurting. 
Me and my boyfriend practiced safe sex, I'm on the pill and he wore a condom. We are both 21 and from very strict family's so we don't talk about this sort of stuff with them. We have stopped having sex untill we are married because we are worried. 
Can someone please explain how this all works . Could I still bleed each month and be pregnant.. Someone said on here their mum bleed for three months and turned out she was pregnant with negative tests. 
Would a test show positive if I tested nearly once each week since the end of March?
I went to my doctor and they said if I have periods and negative tests I'm not pregnant and there is no need for bloods.they didn't really explain much to me, But I would like to know how it all works for knowledge for the future.