Financial talk

i am pretty sure i ovulated on 6march, today im 12 dpo when would be the best time to test..without wasting money??! On 10dpo and 11dpo i had very bad "stretching" like cramping feeling across my lower abdominal.....and kept getting twinges on my right hand side, very lower abdominal....i went docs yesterday and he said its not my appendices but could be my IBS....could it be just my IBS or could I be pregnant? I said to the doc i might be pregnant and he said when and if you miss your period for over a week then come back and see him...what do you think??? the cramping has stopped now and af is due on 20 feb...oh and my boobs feel massive, apart from that no other symptoms! im in the UK - do the pound shops here sell pregnancy tests??