Hormons/Pregnant/Thyroid/Rheumatoid arthritis???

[Zo94]

Hey guys,
I was wondering if any of you have some experience on this.
I had a baby in October, was bleeding for about 6 weeks and when baby was around 3 months I had some bleeding for 2 days and then again the same 2 weeks later. After that I had a 'normal period' kind of..
And now I'm 10 days late.
I did pregnancy tests (2) and both were negativ. I went to the GP too but she only told me to keep on doing tests every week until i have my period again...
Now I have to add that I never had enough milk and when my baby started teething he rejected BFing altogether so I'm not BFing since he's 3 months old (now he's over 4).
We always use protection so it would be shocking if I was pregnant again..

Another thing is I have constant lower back pain even before I got preg but now it's even worse, since my mum has r. arthritis I'll be tested for it + thyroid. Does this have to do something with the period problems?
Any advice would be apprechiated. Thanks!!